Migrate from low-level OSGi API to Declarative Services

One of the main changes to improve the project maintainability is to generalize the use of the Declarative Services best practice.

This task consists in migrating the functionality implemented with the OSGi API to be implemented based on Declarative Services spec.

The main benefits would be:

• Code easier to test: low-level OSGi code is hard to test because it mixes up the business logic with boilerplate code that is necessarily present merely to make the code work.
• Code easier to understand: the business logic mixed with OSGi API is difficult to understand, except if you carefully read and analyse it.