- added network and port models into the l2network plugin instead of using quantum...

- added network and port models into the l2network plugin instead of using quantum models
- added api methods for network and ports
- restructured code to use the l2network network and port
- added l2network base class for other tables to inherit
- added support for l2network plugin model objects to behave like dictionary (gets rid of code to convert objects into dictionaries)
- added foreign key constraints to l2network plugin model attributes representing columns
- added attributes to represent relation between models in l2network plugin
- added joinedload only to network and port (need to to for others)
- added InnoDB as the storage medium in base table for imposing foreign keys
- updated l2network test cases to handle foreign key constraints