Fix/test pre key generation
Move crypto things to js/crypto.js
More wholesale conversion to promises
Refactor some low-level crypto things
Added some shiny new styles

And started splitting up css into multiple files for sanity's sake.
Add Backbone Message(s) model/collection with local storage extension.
Save received messages in Whisper.Messages

This will assign a unique id to the message and save it to localStorage.
First step towards automatically updating views.

I've left the messageMap stuff in place alongside it for now.
Add Backbone-based view to popup.html

Automatically updates itself when new messages are saved to
Whisper.Messages db from the background page.