Move local collection management from companion objects to LocalDataStore

[rfc2822]

Purpose

Refactors the code by relocating the management of local collections from companion objects to a dedicated LocalDataStore interface + implementations.

Goal is to explicitly define who is responsible for managing (CRUD) local collections (address books, calendars etc). Usage of DI allows to fetch settings in the specific implementations, which makes calling classes like the Syncer sub-classes much shorter.

TODO:

• simplify repeated Collection → Service → Account query
• tests

Short description

• Define a new LocalDataStore interface, which is responsible for managing local collections (= the ones accessed over a content provider).
• Implementations for address books, calendars, jtx Board collections, tasks.org task lists.
• Move as much unstructured code from companion objects to a location where it belongs to.

Checklist

• The PR has a proper title, description and label.
• I have self-reviewed the PR.
• I have added documentation to complex functions and functions that can be used by other modules.
• I have added reasonable tests or consciously decided to not add tests.

[rfc2822]

@sunkup Can you please have a look and adapt the tests? (SyncerTest etc.)

[sunkup]

@rfc2822 I have fixed the tests using mockk injection - which is really cool I think. There is some small stuff left, but it looks really good to me otherwise and sync seems to work just fine.

[rfc2822]

Incorporated the suggestions.

I wonder how/whether we could test the stores as well. If you have ideas, please go ahead @sunkup

[sunkup]

Incorporated the suggestions.

I wonder how/whether we could test the stores as well. If you have ideas, please go ahead @sunkup

I will mockk around some more ;)