- progress on migration to CockroachDB (partial)

- partial code implementation

- updated manifest
- corrected README.md notes
- corrected script run-tests-locally
- partial code implementation

- updatd EventsCollector get_events
- added field created_at in ContextModel
- added ChangeFeedClient
- WIP arrangements in unitary tests
- WIP arrangements in ServicerImpl
- arranged run_tests_locally script

- reviewing integration with CockroachDB
- reviewing context REST API
- reviewing database schema
- reviewing code

- 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.

Factorization of code between services and minor unitary testing improvements. (Not finished, it is just a backup)

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

Common:
- reorganized Database API to enable extension of Context API with entities (e.g. Service)
- solved minor bugs in Database API

Context and Device services:
- rearranged services and unit tests according to mentioned Context API changes

Service service:
- initial release (under development, this is just a backup of code)

Common:
- renamed report_coverage.sh script to report_coverage_all.sh

Common/DatabaseAPI:
- improved root class validations and test units
- added _RootEntity interface
- improved definition of Context database API entities

Context service:
- added AddLink/DeleteLink rpc methods
- temporarily disabled integration tests

Device service:
- applied renamings in service and test units

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

This reverts merge request !3

Move database to common folder, since it will be used also by device service, and implement very minor changes.