Create a ContentProvider

[przybylski]

And implement this backend as Provider, this way it can be more consistent with platform and easly extendable.

(original title:Move cache backend to database instead of filesystem)

[mauimauer]

Hmmm...not sure about that. I'd say using SQLite for our kind of application is overkill. Additionally we rely on several non standardized data sources that could change at any time. I'd rather fixup a POJO than managing/migrating SQL tables. Having a content provider is nice an might be something for the roadmap. But it's certainly no pressing issue.