Allow the app to continue in background even when swiped away.

Hello.
I often tend to close all background apps to free up memory, but with KPDX, doing so closes the database.
AFAIK there's no setting to allow the app to daemon-ify.

Start by investigating how KeePassDX handles Android app and database lifecycle when the app is swiped away; the issue names no files or tests. Confirm the expected background behavior with the project before implementing, and define done as preserving database availability after the app is removed from recent apps.

Written by the indexing model from the issue text.