Bug 898352 - Implement homescreen rocket bar and opensearch.

This pull request implements "rocketbar", a search bar on the gaia homepage. The rocketbar will currently search:
* Apps on the device
* Web results from Google, Wikipedia
* Apps from the marketplace
* Web results from Everything.me

Also implemented, but turned off are "Smart Folders". These folders define an open search query, and search Marketplace and Everything.me apps for the query when opened. In order to do this I've moved around some Homescreen Icon code a bit. There is now a "FolderIcon" and "AppIcon" object which inherit from the generalized Icon object.

Everything.me and Marketplace results currently leverage a proxy on my server to handle augmentation of their search APIs. This is only temporary as the final result will be using a standardized opensearch result directly from their servers.