Persist rules: Use Repository Pattern to decouple implementation

[MattHag]

Is your feature request related to a problem? Please describe.
The rule persistence implementation is tightly coupled with the remaining code and is hard to replace for testing. Also refactoring is prone to errors due to its tight coupling with the remaining system.

Describe the solution you'd like
Apply the Repository Pattern to avoid direct dependency on the rule storage implementation. Instead, pass the dependent (dependency inversion principle), so any implementation can be used at runtime and only needs to satisfy the interface.

Advantages

• The rule storage implementation is easy to replace with a fake for tests.
• A distinct interface makes it easy to replace a component
• Hard coupling of Solaar core and the rule persistence implementation becomes loosely.

Additional context
This leads our way to a layered architecture, which is easy to maintain and well to test.

Information

• Solaar version: 1.1.13