Slight revert from said commit. We really do need the
IncomingPushMessageSignal protobuf at the UI layer, mostly because
it contains the 'source' attribute, without which we don't know
who sent the message.
Also fix a crash when there are no attachments on a message.
The 'sender' field actually holds the recipient for outgoing
messages. Rename that field to 'person', indicating the 2nd
party generically.
Also decouples the thread name from thread recipients at the
view layer, in preparation for group support.
Adds Backbone-based Whisper.Messages model/collection with local storage
extension. Saves sent and received messages in Whisper.Messages instead
of message map. This will assign a unique id to the message and save it
to localStorage.
Adds Backbone-based view to popup.html
Automatically updates itself when new messages are saved to
Whisper.Messages db from the background page.
Added some shiny new styles, and started splitting up css into multiple
files for sanity's sake.
