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. 
Is it ridiculously paranoid of me to prefer not to hard-code a date and instead opt for e.g. `Date.current - 1.year`? You can all tell me, I think I need intervention :cold_sweat: