Removed parent-child relationship for crowdsource_hinter.
- Cherry-picked onto main hinting branch.

Conflicts:
	common/lib/xmodule/xmodule/crowdsource_hinter.py
It is now possible to add hints from Studio.  Instructors can see
the id of each problem in Studio - this is visually ugly, and a
temporary fix.
- Cherrypicked into main hinting branch.

Conflicts:
	cms/djangoapps/contentstore/views/component.py
Drop-down menu for selecting target problem for hinter.
- Cherry-picked onto main hinter branch.

Conflicts:
	common/lib/xmodule/xmodule/crowdsource_hinter.py
Feeding a list of problems to Studio is now less hacky.
In the studio editor, only problems on the same page are displayed as
target problem choices.

Added a url for the hint manager in studio.
Fixed link.
Fixed tests for studio hint authoring.
Fixed bug: Impossible to pick hinting target problem if there is only one problem on a page.

Added instructor-facing documentation.
Added graceful failure if we can't find parent module of hinter.