Exports - Add new domain classes for the transformers

Created Transformer, Transforms and UserTransforms domain classes.
Added some code into Bootstrap.groovy to populate new refdata used by those tables.
Exports - Add the Transformers to the application

- Added some script in Bootstrap.groovy to automatically add new Transformer and Transforms
- Create Transformer Service which manage the HTTP connection with the transformer
- Added 2 field in the Transforms table: return_mime and return_file_extension
- Modify Controllers and Views to manage transformers:
The transformation will be called when the 'transforms=<transforms_id>' parameter is in the request.
It will then call the transformer service to trigger the URL and pass the built xml or json file.