Removed uneeded api/base_controller.rb

* Changed api/messages_controller.rb now inherits from the application
* controller
Changed routes to make the intent of api more clear

* "messages#show" route should include the :track_id in the url
Removed .to_a.first from error message returned by render_create_error
method in MessagesController

* Reason for change - the field causing the validation error now serves
* as a key in the error hash: "{\"error\":{\"track_id\":[\"can't be
* blank\"]}}"
Merge branch 'master' of github.com:kareemgrant/backchannel-messages