Several changes:

Common:
- implemented ServiceException class
- updated attributes in entities belonging to Database API
- implemented test method to populate database with example topology

Context service:
- updated genproto script
- implemented report_coverage_context script
- moved specific rest scripts to root folder
- minor arrangements in ContextClient
- updated proto python files
- implemented GetTopology RPC functionality
- implemented unitary testing for GetTopology

Device service:
- updated genproto script