CORE+RPC: added getRequiredAttributes() for resource and list of
services

CORE:
- Added getRequiredAttributes() for resource and list of service.
  Will be used in CreateResource wizard in GUI.
  There is FIXME/TODO for someone to add proper Bl and Impl
  implementation.
- Fixed typos in javadoc above some methods.

RPC:
- Added support for same method.
Merge pull request #105 from zlamalp/core

CORE+RPC: added getRequiredAttributes() for resource and list of services