Refactor the Install Generator a tad.

* Prefer global rescue to begin/rescue.
* short circuit return instead of unless block.
* extract ember-data channel to a method.
* condense ember/ember-data file fetching to one method.
* move private declaration to correct indentation.
Merge pull request #206 from patricksrobertson/pr-generator_cleanup

Refactor the Install Generator a tad.