Changed voting dialog to only display one tab per answer.

No tests for this, yet.

Conflicts:
	common/lib/xmodule/xmodule/crowdsource_hinter.py
	common/templates/hinter_display.html
Fixed tests to work with new vote-tabbing method.  Fixed some string-int incompatibility errors.

Conflicts:
	common/lib/xmodule/xmodule/crowdsource_hinter.py
	common/lib/xmodule/xmodule/tests/test_crowdsource_hinter.py
Refactored formula response grader to expose formula-evaluating to outside world.

In preparation for adding hints to formula response.
Hinter now works with formula responses.  Tests broken.
Crowdsourced hinter now supports formula responses.  Tests still broken.
Fixed numerous 500 errors that result from mal-formatted post requests.

Fixed tests to work with symbolic answer changes.
Changed hint voting ui to show all hints on one page.

Fixed broken tests for hint manager.
Fixed monkey-patching persistent state bug.
Got rid of answer signatures - these don't work with approximate answers at all.  Instead, implemented comparison-based hint matching.

Tests are broken, hint manager is probably broken.
Fixed tests for removing hash access to hints.  Fixed instructor view for same.
Fixed a bug in recording hints shown.

Removed the answer display next to voting.  (This was deemed distracting.)
Added comments to explain confusing field names in crowdsource_hinter.

Fixed some pep8 errors.
Added tests for validate_answer in response types.
Removed parent-child relationship for crowdsource_hinter.
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.
Addressed pull request comments.
Drop-down menu for selecting target problem for hinter.
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.