Move to RSpec 3

Guys,

this is a big change! :sparkles: That was the main changes:

- Update to RSpec 3.1
- Add rspec-its and rspec-collection_matchers to keep the specific matchers
- Update capybara to run features on the new firefox version
- Create the rails_helper
- Disable all RSpec monkey patching
- Using only the new RSpec syntax, no more `should`
- Using only the new RSpec syntax on the mocks and stubs
- Remove some unused stubs, since RSpec now warns about this

Since it involves a lot of spec files is a good idea to check/merge this ASAP since all new features you guys will work will have the old RSpec syntax.

I hope you guys enjoy :fireworks:.