Port d1b057a0ac to glitch-soc

Port 44a7d87cb1 to glitch-soc

Signed-off-by: Claire <claire.github-309c@sitedethib.com>

Port 2d9a85db6e to glitch-soc

Signed-off-by: Claire <claire.github-309c@sitedethib.com>

Port 1bd00036c2 to glitch-soc

Signed-off-by: Claire <claire.github-309c@sitedethib.com>

Port e82467ca41 to glitch-soc

Signed-off-by: Claire <claire.github-309c@sitedethib.com>

Port d2528b26b6 to glitch-soc

Signed-off-by: Claire <claire.github-309c@sitedethib.com>

Cherry-picked d2528b26b6

Conflicts:
- `app/serializers/initial_state_serializer.rb`:
  Upstream changed stuff, we had extra attributes.
  Applied upstream changes while keeping our extra attributes.
- `app/serializers/rest/instance_serializer.rb`:
  Upstream actually moved that to `app/serializers/rest/v1/instance_serializer.rb`,
  so updated that file by keeping our extra attributes, and took upstream's
  version of `app/serializers/rest/instance_serializer.rb`.
- `spec/views/about/show.html.haml_spec.rb`:
  Took upstream's version.

* Remove timeline preview link from nav panel when not signed-in

* Always enable server stats