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

Conflicts:
- README.md
  discarded upstream changes
- app/controllers/api/v1/bookmarks_controller.rb
  finally merged upstream, some code style fixes
  and slightly changed pagination code
- app/controllers/application_controller.rb
  changed upstream to always return HTML error pages
  slight conflict caused by theming code
- app/models/bookmark.rb
  finally merged upstream, no real conflict
- spec/controllers/api/v1/bookmarks_controller_spec.rb
  finally merged upstream, slightly changed pagination code

app/controllers/application_controller.rb

@@ -211,13 +211,7 @@ class ApplicationController < ActionController::Base
   end
 
   def respond_with_error(code)
-    respond_to do |format|
-      format.any  { head code }
-
-      format.html do
-        use_pack 'error'
-        render "errors/#{code}", layout: 'error', status: code
-      end
-    end
+    use_pack 'error'
+    render "errors/#{code}", layout: 'error', status: code
   end
 end