Merge remote-tracking branch 'upstream/develop' into polish

* upstream/develop:
  i18n: make "plain text" translatable
  add the ability to select a post's content type

src/i18n/messages.js

@@ -400,6 +400,9 @@ const en = {
       unlisted: 'Unlisted - Do not post to public timelines',
       private: 'Followers-only - Post to followers only',
       direct: 'Direct - Post to mentioned users only'
+    },
+    content_type: {
+      plain_text: 'Plain text'
     }
   },
   finder: {