Default database (h2) is not closed when running gradle wrapper with daemon

[g3force]

After running a command, e.g. gradlew uS, a file called 'seuac.lock.db' remains in the seubase. This indicates that the database is not closed.
This leads to problems when gradle is not reusing a daemon for some reason.

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Thank you! 🙏

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[lreimer]

Currently we use a shutdown hook to close the DB.
We need to replace it with explicit open() and close() methods on the database provider instead.

Thank you, everything looks good now!

[g3force]

This will be fixed with #57