Code review request for gadget-ui-editor

Branch name: gadget-ui-editor

Link to the relevant commit(s): 
https://code.google.com/p/oppia/source/detail?r=55749c1c9114a83362182d54f7ce99ff
0c553543&name=gadget-ui-editor#

Purpose of code changes on this branch:
- Consolidated to a single factory that maintains state for gadget instance 
details and their locations across panels.

When reviewing my code changes, please focus on:
- Suggested two factory methods I think we can remove from 
explorationGadgetsService based on the new consolidated service. (see inline 
comments in code) Thoughts on the best consolidated API?
- Any feedback on the new service or its new private methods.
- Any suggestions on overall implementation in general.

After the review, I'll merge this branch into: Nothing yet. Still working 
towards first end-to-end functional implementation.

@Vishal, please feel free to help implement any improvements on this branch 
when you get in. Let me know where you leave off so I can help JP time.

Original issue reported on code.google.com by anu...@google.com on 26 May 2015 at 7:30

danieljjh / oppia

Code review request for gadget-ui-editor #781