Filtering categories in collections

- added method to get all categories related to a given category from a collection
- improved get method in model to use new filtering method of collection
- added and updated methods in client to allow retrieval of all entity, resource and link types and type identifiers
- added and updated rspec tests for collection and model
Category filtering for OCCI binary

- added option -F and --filter to occi binary options
- added category filtering to occi binary when dumping model
Merge pull request #35 from ffeldhaus/feature-filtering

Filtering categories in collections