As a user, I want to be able to download and apply new homescreen apps so that I can customize my device experience.

Acceptance Criteria:
1. I am able to download new homescreens from Marketplace.
2. I am able to download new homescreens from third party marketplaces.
3. Upon download completion, I can apply the new homescreen.
4. If I don't like the new homescreen, I have a way to revert to my previous homescreen without having to go find the homescreen section of Settings.
5. Reverting to my previous homescreen restores the old homescreen in the configuration (app layout, wallpaper) that it was in previously.