Remove thing_menu_menu which is not needed anymore

Copy the remaining items that need to be dealt with to thing_frag_menu.
Issue #207: change saved icon visibility condition
Rename joined saved and vote columns
Create new loader for ThingFragment

Extract BaseAsyncTaskLoader from AccountLoader and use that base class
for loading the ThingBundle for ThingFragment. The loader will be used
to fetch info about a thing when it is missing like when just a raw
url is provided.