Bridgedomain capab getters

### VLANBridgeAPIHelper

- Parser methods to build API classes from Model information.

### VLANBridgeCapability

- Implementation of getters for this capability.

### ModelHelper

- Helpers to get BridgeDomain from Hostedcollection association.
- Helpers to get BridgeDomain by name from HostedCollection association.

### [ Issues ]

http://jira.i2cat.net/browse/OPENNAAS-1344
http://jira.i2cat.net/browse/OPENNAAS-1368