Add `app.import` to control legacy files, remove broccoli-bower.
better implementation of defaults in `EmberApp`

Lets loader + wrapInEval also be configurable.

We plan soon to make loader configurable via the underlying filter.
Please note, the current setup still does not allow this.
Use local trees instead of hardcoded folders.
Handle styles from `app.import`.
Allow populating only parts of `trees`.

Defaults only allows single depth merges.
Merge pull request #562 from rjackson/remove-broccoli-bower

Add `app.import` to control legacy files, remove broccoli-bower.
Install phantomjs when testing with master
phantomjs is needed by default going forward
Merge pull request #602 from dustinfarris/testing-with-master

Mention PhantomJS requirement for testing
Revert "phantomjs is needed by default going forward"

This reverts commit 6800ee37496428b47b5a723b4fee61c792c8bc12.
This reverts commit 12ea16de34c314f86b8c45baaec4401d3d3412b9.