Fixing two issues with the previous commit: i) obtaining the correct service gRPC port; ii) updating the gitlab ci file to use the correct service port.

Integration of Service service, multiple improvements in Context and Device services, and GitLab CI pipeline integration and functional tests

See merge request teraflow-h2020/controller!12

Common / Context / Device / Service:
- Improvements in unitary testing
- Extended assertion validators tor testing
- Factorized service implementation code to improve testability, reusability and increase code coverage

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

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)

Several improvements

See merge request teraflow-h2020/controller!11