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.
Currently experiencing a few problems:
1. Tons of errors on app start. It's as if Jazzicon is getting called many times at start with some object as its diameter.
2. Weird visual glitches. When leaving a view with a jazzicon, it flashes off its border radius.
3. Messy transitions. Might want to just re-do the transitions. They just look awful, it's barely worthwhile.
