Fennec Work: pull database back-end, replace with pure file-based storage

Fennec will not allow the use of a database for a minor feature such as this, the overhead of a DB is too great, and existing use of a db was there for convenience.

Unfortunately, this required a rather hefty refactor. The bonus being, a lot of the problems with missing uploads and disappearing data should be gone. I hope. 

As part of this, MozStumbler client is now using the same upload method as the stumbler service, which does not use Android sync.