Refactor the code that maps a cue to a region.

Update RegionBoundingBox to be able to detect if it should add
a cue to itself or not.
Don't run processing model tests by default in util.js

This was causing us to run the processing model many times when
running processing model tests instead of just running it once
like we need too.
Refactor FakeWindow a bit.

- Document's should have a 'body' property that we can attach
  overlays to in the future in order to get the computed style.
- TextNodes shouldn't have styles or child nodes.
- ProcessingInstructions don't need styles.
Add support for PhantomJs tests.

Added a simple PhantomJs test.
Update PhantomJS tests to address review comments on #122.
Style fixes in PhantomJS tests.