fix: allow reuse of a database name

[J4Wx]

This closes #554

Some changes:

• When creating a database, unique is only checked against rows where deleted_at is null.
• When deleting a database that has backups, the state of those backups is set to a new state, "stopped", to as to better represent that they've stopped running in the UI rather than them entering an error state on the next run.
• In the backups list a backup belonging to a deleted database has the name displayed in red and with a trash can icon, on hover the deleted_at is shown in the tooltip.

Thanks to @dyanakiev for helping me understand the implications of this change.