Add gem appraisal

* test against Rails 4.0 and Rails 4.1
* tell TraviscCI about appraisals
Use Dummy::Application in environment loaders for Rails 4.0 comp ability
Further Adjustments for compability with Rails 4.0
Keep spec/dummy/db directory
Maintain test-schema for Rails >= 4.1
Merge branch 'test_against_different_gemsets'

Closes #3