First functional version of Service with Service Handler for L3NM-Emulated services using Emulated Devices

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)

Context service:
- corrected port numbers

Device service:
- corrected port numbers
- upgraded gitlab-ci configuration

Preliminary unfinished version of device service and Context API based on Redis. To be finished, it is just a backup.

This reverts merge request !3