Purpose

Right now, we are always returning Result.success() in BaseSyncWorker, even if ProcessEventsTask fails. There should be proper error results.

Short description

Added a return type to ProcessEventsTask.sync, if the synchronization is successful (exception is null) returns true, otherwise returns false.

Then, the result is received by BaseSyncWorker, which then if any of the subscriptions returns false while synchronizing, outputs Result.failure, otherwise Result.success.

Tests added:

• One simple synchronization test, which takes an ICS file from resources and runs the worker with it. The result is expected to be successful.
• Another test which adds two subscriptions: the same local one as before, and a remote one which doesn't exist.
  The result is expected to be a failure because even though the first subscription is synchronized correctly, the second one fails.

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.