Lots of changes here:
* rake draper:install no longer needed
* don't generate an ApplicationGenerator by default
** If one exists, the generator respects it
* Fixes#53
- run rails g draper:install to create draper directories (app/decorators and spec/decorators), along with application_decorator files.
- use rails g draper:install -t=test_unit to select unit tests instead of rspec.