Fixes#197
Also as a side effect, by creating this `iconFactory.cache` object, we have a convenient place for specifying stock icons for known contracts!
We can just hard-code image addresses in the `ui/lib/icon-factory.js` cache instantiation, and those values will be injected into the identicon image tag `src` attributes.
Calls to `eth.sign` are now transiently persisted in memory, and displayed in a chronological stack with pending transactions (which are still persisted to disk).
This allows the user a method to sign/cancel transactions even if they miss the Chrome notification.
Improved a lot of the view routing, to avoid cases where routes would show an empty account view, or transition to the accounts list when it shouldn't.
Broke the transaction approval view into a couple components so messages and transactions could have their own templates.
