Port f978afa487 to glitch-soc

Port f7a6f9489d to glitch-soc

[API] [vanilla required] [glitch-soc optional] initial_state show_sensitive_media boolean changed to show_media string with options "default", "hide_all", "show_all"

Port ac092d03e7 to glitch-soc

- Preload video metadata if the video is loaded in detailed view, as it is
  likely to get played, and metadata is useful for seeking in the video.
- Preload video data if it's fullscreen as it is extremely likely to get
  played right after being put in fullscreen (although those are two steps).
- Preload video data if the user has clicked the position slider, as the video
  will play as soon as the mouse button is released, and video metadata is
  needed to properly seek into the video.

This prevents accidental text selection and avoids opening the toot containing
the video in the dynamic column when clicking on the position slider.

Port d9b2f84c92 to glitch-soc

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 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

Port the UI part of 76f3d5d16b to glitch-soc