Merge branch 'fix/error-pages' of https://github.com/ineffyble/mastodon into ineffyble-fix/error-pages

Add a default missing.png header image - fixes #492

Call uniq on the string version of mb_chars tags - fixes #503

Show visibility toggle on videos, show regardless of sensitivity

Don't show loading bar when re-loading already loaded status. Don't even try to fetch ancestors from DB when in_reply_to_id is nil

Also, since the root component connects to the stream that updates home/notification columns,
there is pretty much no case for refreshing those columns beyond initial load. So, move the
loading of those columns into the root component, to prevent unneccessary reloads when switching tabs
on mobile or resizing desktop window between mobile/desktop layouts

Add Heroku deployment support

Show 'do not display in public timeline' when replying to self