Organizations CRUD

Adds organizations crud operations according to the user story from PT:
https://www.pivotaltracker.com/story/show/77974308

Accessible on Heroku instance: 
http://sleepy-reef-7794.herokuapp.com/admin/organizations

Implements organizations crud with cucumber tests (similar to the ones for partners) and rspec tests for the model. 
@NikitaAvvakumov - sorry, I am not sure I understood all of your points. Please, take a look at the current version if I managed to handle this right.