Merge pull request #54 from kcarcia/validation

Fixed ajax problem on registration form.
Users can 'enter' to continue on assignment code form.
Merge pull request #55 from kcarcia/acode

Users can hit 'enter' to continue on assignment code form.
Update timestamps when students opens a lab and submits a lab.
Merge pull request #56 from kcarcia/acode

Update timestamps when (1) students opens a lab and (2) submits a lab.
Fixing enter key issues with registration and acode forms.