Merge branch 'master' into glitch-soc/merge-upstream

Conflicts:
- `Gemfile.lock`:
  Not a real conflict, just a glitch-soc-only dependency too close to a
  dependency that got updated upstream. Updated as well.
- `app/models/status.rb`:
  Not a real conflict, just a change too close to glitch-soc-changed code
  for optionally showing boosts in public timelines.
  Applied upstream changes.
- `app/views/layouts/application.html.haml`:
  Upstream a new, static CSS file, conflict due to glitch-soc's theming
  system, include the file regardless of the theme.
- `config/initializers/content_security_policy.rb`:
  Upstream dropped 'unsafe-inline' from the 'style-src' directive, but
  both files are very different. Removed 'unsafe-inline' as well.

app/controllers/api/v1/timelines/public_controller.rb

@@ -39,7 +39,7 @@ class Api::V1::Timelines::PublicController < Api::BaseController
   end
 
   def public_timeline_statuses
-    Status.as_public_timeline(current_account, truthy_param?(:local))
+    Status.as_public_timeline(current_account, truthy_param?(:remote) ? :remote : truthy_param?(:local))
   end
 
   def insert_pagination_headers
@@ -47,7 +47,7 @@ class Api::V1::Timelines::PublicController < Api::BaseController
   end
 
   def pagination_params(core_params)
-    params.slice(:local, :limit, :only_media).permit(:local, :limit, :only_media).merge(core_params)
+    params.slice(:local, :remote, :limit, :only_media).permit(:local, :remote, :limit, :only_media).merge(core_params)
   end
 
   def next_path