- "billing" worksheet action
Merge remote-tracking branch 'upstream/master'
Merge pull request #167 from adamarla/master

Added controller action
 minor styling changes
 minor styling changes
 minor styling changes
Resolved conflicts on merge with Github
Conflicts:
	app/controllers/tokens_controller.rb
Corrected migration error on Heroku ...

The problem was because in an earlier migration, a model method was
being called that now references the re-named GradedResponse table.

However, the migration for renaming GradedResponse does not come
until later.
As a result, we were getting a nil object in the earlier migration.
Hide fdb-controls on hover and re-appear when mouse goes out

This is to give the grader a clear view so that in case he wants
to start a long comment from somewhere under fdb-controls, then he can
Returning the quality of an attempt ( as weak, medium, strong, red ) ...

Changes in d3-charts styling to reflect the above