Port 64d7a63f18 to glitch-soc

Port bd0791d800 to glitch-soc

See also the following commits:

- 0c3ce41031
- 268d90e810

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.

Port 86efccce2a to glitch-soc

Port 45c9f16f71 to glitch-soc

Port b1938d7853 to glitch-soc

Port 3523aa440b to glitch-soc

Port cbf97c03bb to glitch-soc

Port 9a1a55ce52 to glitch-soc

Port b0664a5e6c to glitch-soc

Port missing part of 6ae70a92c9 to glitch-soc

Port fa04945365 to glitch-soc

Port missing changes from 4e4f1b0dcb to glitch-soc

Port 0128b86d30 to glitch-soc

Port 2587fcdd27 to glitch-soc

Port d9b2f84c92 to glitch-soc

Port 53c2164e9c to glitch-soc

Port 904a2479dd to glitch-soc

Port d1f34151ae to glitch-soc

Port d185f3ddaf to glitch-soc

This doesn't change anything for glitch-style fields, but those will go
away eventually

The rationale behind this is that if the user wants to report violent media,
they might not want to see it repeatedly. The “sensitive” property is still
kept, displaying different messages for hidden media depending on whether
they are marked as sensitive.

Port c88e12fca6 to glitch-soc

Port ad5d3134e4 to glitch-soc

glitch-soc-style still in backup, both sharing the same SCSS style

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

Backports daefbd66a6

Port ff7941e652 to glitch-soc

Port the display part of the following commits to glitch-soc:
* 90f12f2e5a
* b170627ceb
* 11697d6894
* 56eb5c3f34

Port the video-player part of 036dd98abb to
glitch-soc. MediaGallery part ignored since it has diverged quite a bit.

This fixes #423

Port ecdac9017e to glitch-soc