Register gem as a valid payment engine for Neighborly

Uses new Inteface class to define how Neighborly should interact with
the payment engine.
Remove fallback for BRL when registering engine

If happens to currency_charge configuration not exist, we want the
initialization to fail.
Use current interface for payment engine needed by Neighborly
Delete files related to Moip integration
Normalize existing locale files
Complete purchase of any resource using "#{resource_name}_id" param

Includes a refactory in its tests.
Process return from PayPal
Use flash.alert helper to show error messages to user
Move IPN related specs out of setup block
Fix erroneous use of configuration when refering to payment_method
Refactor specs related to PaypalExpressController#gateway
Handle matches or contributions when searching for a resource
Update Rspec syntax of mocks
Update interface expected of payment form
Remove failing specs

With the recent refactorying in the specs of this controller, these
specs started to fail, simply because their "setup" method was raising
the exception in the wrong place. So, these specs should not (now nor
before) pass.
Add additional and inclusive calculators of fees
Provide view for payments in current format required by Neighborly
Use HashWithIndifferentAccess to search for payments
Merge branch 'im-new-engine-interface'
Select between calculators when charging the payment