used from nginx when Rails fails.

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

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

Change boost sprite to look like fa-retweet