Validate student profile name field, use Backbone.js on the profile page

Changes:
* Validate student profile name field.
* Use Backbone for student profile JS.
* Use the same HTTP endpoint for both reading and updating profile info.

Reviewers: @AlasdairSwan @rlucioni 
FYI: @andy-armstrong 

[ECOM-409](https://openedx.atlassian.net/browse/ECOM-409)