Initial layout for offline guides status

Still needs lots of work to display accurate and realtime data as well
as making it pretty.
Store and display last sync time
ApiDatabase: Remove outdated comment

It actually _is_ used now =P.
OfflineGuides: Update ProgressBar style

Now it uses the appropriate style based on the OS version.
ImageSizes: Refactor definition in resources

This makes them named string resources so the large version overrides
only what is necessary.
ImageSizes: Refactor into static properties

It's much much easier to just have static properties on ImageSizes that
we set once and can use globally.
Offline guide view: Fix query result

Turns out refactoring the getGuideFromCursor method resulted in a bug
that caused it to always return null. The Cursor must be positioned to
the first element in order to get any meaningful data out of it.
ApiDB: Change site name column to siteid

Integers make more sense and siteid is more reliable.
Fallback to original image if .huge doesn't exist

We already did this but it didn't work for offline guides. This shuffles
some code around so we can easily download the original if the huge
fails and display the original offline version if it fails when viewing
an offline guide.