(+) Locally persistent posts integrated with UI

-user posts can be stored and retrieved from the db through the UI
-some fixes in the db (do not close cursor before reading), return
empty lists instead of null if there are no results.
-keep the list of friends updated.
-unify db interface w.r.t. to putPost: since Post now holds wallOwner
some arguments have become obsolete.
Merge branch 'local-posts'