* feat(components/media_gallery): Responsive images

* fix(components/media_gallery): Link to image URL

This also resolves the issues where sometimes the timestamps wrap and also sits unpleasantly close to the … button.

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

Avatars now have consistent styling across all pages; border radius can be adjusted with a SASS variable ($ui-avatar-border-size)

* Replace TextIconButton for SensitiveButton to IconButton

* line-height

* Unread indicator was invisible behind column header, adjusted

* Unread indicator now a CSS pseudo-element

* Adjust flex

* Re-add clear notifications button

* remove connect() in column_settings

* one line

* remove unused props

before the full-size image is loaded

* Add regex filter on the community timeline and the public timeline

* correcting

* Adjust the height of header buttons

* Remove trailing spaces

* Remove trailing spaces

* Solve some code duplication

* reset the state of the locale files in app/javascript/mastodon/locales

* adjust to upstream

* adjust to upstream

* change keys of locale settings

* Add support key shortcut to Onboarding Modal

* this.state.pages -> this.pages

* 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

* Remove react-imageloader

* add eslint-disable-line

* improve image loading experience

* remove unneeded import

* use PureComponent

* Use componentWillMount instead of constructor

The combination of object-fit, relative position 50% from top and translating it
back upwards 50% is what allows us to crop the video properly, so it needs to
be +50%-50%

on status fade-in, fix buttons not having pointer cursor

Fix warning for ESLint (jsx-a11y/href-no-hash).

Fixes #3277. I've tested in QupZilla on Mac and can confirm it fixes the issue, and that Chrome 58 is not affected (because it has Grid).