Modify backend parsing helpers to add calling context.

When data from the backend fails to parse as we expect a BadJson
exception is thrown. Until now it's been difficult to know the context
of this error in terms of the backend end-point URL that producted the
data in for first place. The response parsing helpers now accept a
context param which can be provided to give the calling context and
provide it to the ultimately thrown exception.
Add backend method to efficiently access a user's activity
Add a test for backend JSON error context
Remove unneeded and accidentally committed methods
WIP getting user activity to page properly
Another pagination/list handling overhaul...

 - Attempting to combine paging/offset for bounded and unbounded
   lists (search results, activity streams) did not work well on
   the backend since it broke the ability to fetch "one more" than
   the needed number of a stream to check if there was any more
   content.
 - Introduced RangeParams handler to deal with this for unbounded
   streams. PageParams converts page into offset for the backend,
   RangeParams uses the offset directly.
Add new infitite-pageable user activity list.
Cleanup how pagination namespacing is handled in templates
Merge branch 'master' into virtual_collection_rework

Conflicts:
	modules/core/app/backend/rest/RestSocial.scala
Fix compilation issue related to pagination reworking