Remove duplicate codes from EntrepreneurControllers.

...by promoting Entrepreneur lookup codes to the superclass,
BaseController.
Add an AbstractEntrepreneurController.

These three controllers share the same characteristics: they need an
Entrepreneur to be present. So to better enforce rules and other stuffs,
we create an AbstractEntrepreneurController to group these controllers
together:

  * EntrepreneurAccountController
  * EntrepreneurAgenciesController
  * EntrepreneurRequestsController