Merge pull request #212 from adamarla/master

Few minor fixes
Merge pull request #213 from adamarla/master

Few minor fixes
Disable options if solution already seen, EXCEPT -

... self-check if user made a prior selection. We want to be able to
show them their correct/incorrect selection alongside the solution
Merge branch 'master' of github.com:abhinavc/web-application
flag to suggest if student is enrolled in any sektion
Merge remote-tracking branch 'upstream/master'
exclude problems given as homework from list of Stabs
Provide 100 free gredits to every new student ...

For school students, however, gredits never run out and are auto-topped.
Merge branch 'master' of heroku.com:drona
Changed welcome e-mail to students
 Some more edits to student welcome mail
Added some more query methods
Elminiated hint marker. logic will run off the Revision table instead
Merge remote-tracking branch 'upstream/master'