copy/save/delete is accessed via longpress for all media messages, just
like for simple text messages.
Notes
-----
We don't support saving audio attachments as it's not clear where they should go.
(I don't think users expect them to end up in their iTunes library.)
There is still no UX for "pasting" media into Signal.
Removed the now redundant (and confusing) "share" button interface.
//FREEBIE
9db3b0db27