Foreground import operations are suspended in background state

[vin047]

Describe the bug
Import operations started in the foreground remain suspended in background state. This makes them unable to be set as dependencies (as required by #15) as well as unresponsive to cancellation events until the app returns to the foreground.

To Reproduce
Steps to reproduce the behavior:

1. Enable Debug logs and Backup & Sync.
2. Leave phone on standby and on charge to begin background process.
3. Later, pick up phone and open app.
4. Observe in the logs that the foreground import operations resumed only after app returned to foreground, regardless of other events including cancellation.

Expected behavior
Foreground import operation should resume and complete in background mode (without spawning another operation for the next batch).

Dependent on #17