Merge branch 'master' into glitch-soc/master

Conflicts:
- `README.md`:
  We have different README files. Discarded upstream changes.
- `app/views/layouts/admin.html.haml`:
  Conflict due to glitch-soc theming system.
  Adapted upstream changes.
- `app/views/layouts/embedded.html.haml`:
  Conflict due to glitch-soc theming system.
  Adapted upstream changes.
- `yarn.lock`:
  No real conflict, glitch-specific dependency too close to
  an updated one. Adapted upstream change.

app/helpers/settings_helper.rb

@@ -32,6 +32,7 @@ module SettingsHelper
     hy: 'Հայերեն',
     id: 'Bahasa Indonesia',
     io: 'Ido',
+    is: 'Íslenska',
     it: 'Italiano',
     ja: '日本語',
     ka: 'ქართული',