src: Pass the content type to RefreshDB

Add an array of strings as argument to RefreshDB to denote the type of
content we are interested in indexing.

https://bugzilla.gnome.org/show_bug.cgi?id=728878
Prepare 3.13.3
src: Add a Picasa Web miner based on GData

https://bugzilla.gnome.org/show_bug.cgi?id=728878