Beta Feature: Register mobile skin, offer users the ability to change it

Offer the blue pill or the red pill

* Kill the myth that mobile is a mysterious black box and make it
clear that it is a skin by registering it via Beta Feature
* Allow users on slower connections to have it as a skin choice if
preferred
* Hide uploads link since no equivalent on desktop, and doesn't work
on desktop (due to overlay styling)
* Swap out MobileOptions for Preferences

Deployed to BetaFeatures for time being to allow for the fact there
may be problems in a desktop environment and it may lack some of the
needed polish.

Bug: 36636
Change-Id: If3c896e56de68b50936de7942e376ceadebf096d
Merge "Beta Feature: Register mobile skin, offer users the ability to change it"