* Adds basic GET api support for CustomFieldsets
Currently there is not support for getting what fields a given fieldset contains
from the API. This commit creates a new API Controller for CustomFieldsets as
well as Transformers for CustomFields CustomFieldsets. Additionally, the api
route has been updated so that a show method can be access from
http://myapp/api/v1/fieldsets/{id}
* CustomFieldsetsTransformer only returns id and name of model
* Added index api method for CustomFieldsets
* Removes copy/paste error in CustomFieldsetController (including search)
* Added id to CustomFieldsetsTransformers
* Adds custom_fieldset_id as a field when storing and updating AssetModels
* Removed uncessesary parameter from CustomFieldsetsController.index
* Cleaned up CustomFieldset API
