Tidy the engine for master branch.

- [x] Tidy up the engine.
- [x] Fixed so it has correct manifest assets files.
- [x] Fixed how it copy the assets file, only one file needed if manifest setup correctly.
- [x] Add sample spec (from spree frontend) and setup the spec environment.
- [x] Add Travis and [Code Climate](https://codeclimate.com/github/200Creative/spree_bootstrap_frontend) (you need to setup Travis for this ... Code Climate is kind of pointless in this case but it looks good :dancer: ).

Had to make one test pending (with comment) noticed that the default `css` class definitions has not been preserved, this can breaks other extensions. They probably very few due to that they should rely on hooks, in this case it was `.errors` that was lost.
@200Creative Note you can probably cherry-pick this into the other branches just change to correct dependencies.