- Complete rework of Database API
- Integration of Database API into Context
- Improvement of API

This commit is not a final implementation, just an intermediate backup.

Common:
- minor bug resolutions in Context API

Service:
- first functional version of Service (implementation of GetConnectionList postponed)
- minor corrections in service.proto and related files
- implemented unitary tests

Common:
- Improvements in Database API definition and unit tests
- Implemented additional Assertions to be used by unitary tests

Context and Device:
- Improved logging of errors.

Service:
- Implemented service methods (except GetConnectionList). All methods are under active debug.
- Partially implemented unitary tests