Code review request for gadgets-develop-review

Branch name: gadgets-develop-review

Link to the relevant commit(s): 
https://code.google.com/p/oppia/source/detail?r=df27b1a6328deac028ef88d1c41b9583
8380e9d4&name=gadgets-develop-review

Purpose of code changes on this branch:
- Refactored gadget width/height to use constants.
- Updated front-end validation to prevent saving of gadgets that don't fit 
their assigned panels.
- Updated backend tests accordingly.

When reviewing my code changes, please focus on:
- Anything that stands out.

After the review, I'll merge this branch into: N/A, still working towards full 
branch approval.

Original issue reported on code.google.com by anu...@google.com on 26 Jun 2015 at 11:40

Dev4X / oppia

Code review request for gadgets-develop-review #836