Code review request for gadgets-editable-name branch

Branch name: gadgets-editable-name

Link to the relevant commit(s): 
https://code.google.com/p/oppia/source/detail?r=029cef1ce0cbb7524beb988f53426ac4
7622b92e&name=gadgets-editable-name

Purpose of code changes on this branch:
- Refactor gadgets to have a unique name to distinguish them to authors across 
the Editor UX.
- Initial work on a front-end explorationGadgetsService with APIs to 
add/delete/modify gadgets and to assist with unique name generation.

When reviewing my code changes, please focus on:
- Updated YAML schema to include a new 'editor_unique_name' attribute on 
gadgets. Does the attribute name make sense? Is it necessary to increase to 
schema_version: 6 for this change?  There's would be no difference between 
YAML_CONTENT_V5 and YAML_CONTENT_V6 in exp_domain_test for this minor 
adjustments to gadgets data.
- First pass implementing an angular service (explorationGadgetsService) based 
largely on explorationStatesService. Likely a number of things should be 
different, but wanted to get a WIP we can make progress on. Is this the right 
direction in general?
- Anything else that stands out.

After the review, I'll merge this branch into: develop

Original issue reported on code.google.com by anu...@google.com on 21 May 2015 at 8:23

sanyaade-teachings / oppia

Code review request for gadgets-editable-name branch #772