Implemented strong_parameters for Category/CategoriesController.

Category now requires parameters to be permitted by strong_parameters using #require or #permit for mass-assignment. Missing required parameters now throw a ActionController::ParameterMissing execption instead of the Discourse::InvalidParameters execption.
Implemented strong_parameters for Invite/InvitesController.

The email parameter is now required using strong parameters and will throw ActionController::ParameterMissing if it is missing. If the email address is incorrect or invalid, Discourse::InvalidParameters will still be thrown.
Implemented strong_parameters for PostAction/PostActionsController.

PostActionsController now uses strong_parameters' #require to require certain parameters. ActionController::ParameterMissing is now thrown when a reqired parameter is missing, rather than Discourse::InvalidParameters.
Implemented strong_parameters for Upload/UploadsController.

The topic_id param is now required using strong_parameters' #require method. If the parameter is missing ActionController::ParameterMissing will be raised instead of Discourse::InvalidParameters.
Merge pull request #960 from iancmyers/strong-parameters

Began implementing strong_parameters