Port 5bf100f87b to glitch-soc

So far, glitch-soc used history.length to decide whether to call `goBack()` or
go to / in order to not leave the webUI. This made clicking the “Back” button
go to the “Getting started” column instead of going back in the browser's
history when such an action would leave the web UI, but also when:
- The WebUI is refreshed (F5)
- A tab is restored
- The history length reaches its maximum (e.g., 50 in Firefox)

This commit fixes these shortcomings by checking `window.history.state`.
Indeed, we only want to go back in the browser's history when the current
location has been reached from within the WebUI, which only happens via
`pushState` as far as I know. Since browser store the serialized state in
the browser history, this also survives page reload and session restoration.

Inspired from b6003afcdb but using component
properties instead of redux store for hidden/revealed state.

Port ffb2b8ef8c to glitch-soc

Port 08e4c78e78 to glitch-soc.

SCSS fix inspired by 69f13e7bca.

* Fix #5314

* fix not beautiful code

* fix broken design with mobile view

* remove no longer needed code

* Upgrade to React 16.0.0

* Disable some uncritical tests while chai-enzyme remains incompatible

* added notification cleaning drawer

* bugfix

* fully implemented set operations for notif cleaning

* i18n for notif cleaning drawer & improved logic slightly. Also added a confirm dialog

* - notif dismiss "overlay" now shoves the notif aside to avoid overlap
- added focus ring to header buttons
- removed notif overlay entirely from DOM if mode is disabled

* removed comment

* CSS tuning - inconsistent division lines fix

* fix(compose): Add aria-label for the navigation links

* fix(search): Add input label

* fix(navigation_bar): Link description

* fix(autosuggest_textarea): Add input label

* fix(compose_form): Add input label

* fix(upload_button): Add input label

* fix(account/header): Add link content

* fix(column_header): Use h1 tag

* fix(column_header): Labels move buttons moving column

* fix(settings_text): Add label to input

* fix(column_header): Remove role from h1

* fix(modal_root): Use role=dialog

* fix(modal_root): Focus restauration

* fix(modal_root): Apply inert to sibligs

* fix(column_header): Add role=button

* chore(eslint): Disable jsx-a11y/label-has-for

* fix(column_header): Invalid ARIA role

* fix(column): Remove hidden nodes from the DOM

* refactor(column_link): Remove unused property hideOnMobile

* fix(column_header): Use aria-pressed

* fix(column_header): Make collapsed content not focusable, add focusable property

* fix(column_loading): Make header non-focusable

* fix(column_settings): Use role to group the toggles

* fix(compose): Use nav and remove redundant aria-label

* fix(tabs_tab): Use nav and add aria-label

* fix(app): Add aria-label for settings toggle button

* chore: Run yarn manage:translations

This PR adds a new notification cleaning mode, super perfectly tuned for accessibility, and removes the previous notification cleaning functionality as it's now redundant.

* w.i.p. notif clearing mode

* Better CSS for selected notification and shorter text if Stretch is off

* wip for rebase ~

* all working in notif clearing mode, except the actual removal

* bulk delete route for piggo

* cleaning + refactor. endpoint gives 422 for some reason

* formatting

* use the right route

* fix broken destroy_multiple

* load more notifs after succ cleaning

* satisfy eslint

* Removed CSS for the old notif delete button

* Tabindex=0 is mandatory

In order to make it possible to tab to this element you must have tab index = 0. Removing this violates WCAG and makes it impossible to use the interface without good eyesight and a mouse. So nobody with certain mobility impairments, vision impairments, or brain injuries would be able to use this feature if you don't have tabindex=0

* Corrected aria-label

Previous label implied a different behavior from what actually happens

* aria role localization & made the overlay behave like a checkbox

* checkboxes css and better contrast

* color tuning for the notif overlay

* fanceh checkboxes etc and nice backgrounds

* SHUT UP TRAVIS

* feat: Replace react-swipeable with react-swipeable-views

* fix: iOS 9

* Remove unused column_collapsable.js
* Remove old styles
* Extract `> div`  style to independent class

ref https://tc39.github.io/proposal-decorators/

* chore(yarn): Remove react-router

* chore(yarn): Remove react-router-scroll

* chore(yarn): Remove history

* chore(yarn): Add react-router-dom

* chore: Remove usages of react-router-scroll

* refactor: Upgrade to react-router-web

* refactor: Use fork of react-router-scroll

This reverts commit 2ddea9a6c8.

* fix: Issues mentions in the PR feedback

* Unread indicator was invisible behind column header, adjusted

* Unread indicator now a CSS pseudo-element

* Adjust flex

* Allow mounting arbitrary columns

* Refactor column headers, allow pinning/unpinning and moving columns around

* Collapse animation

* Re-introduce scroll to top

* Save column settings properly, do not display pin options in
single-column view, do not display collapse icon if there is
nothing to collapse

* Fix one instance of public timeline being closed closing the stream
Fix back buttons inconsistently sending you back to / even if history exists

* Getting started displays links to columns that are not mounted