feat: add minecraft container supper, add tags, fix cross deletion

[Silthus]

Hi,

I updated the repo to fit my needs for backing up Minecraft servers and I just wanted to give you the option to pull all or some of the changes upstream.

Here is what I changed:

• fixed #31: restic forget now groups by paths and tags ignoring other backups
• added #6: added the option for database and minecraft containers to add tags via a label
• added a new container type: minecraft. The backup container will stop auto-save via rcon-cli and continue saving when done with backups
• added more options for forget: keep-latest
• added config option to keep certain tags from forget
• fixed crontab validation to validate the complete crontab syntax

[einarf]

Thanks a lot for this. I've had no time take a deeper look, but I'm sure a lot of this can be useful.

I never got around doing a proper cleanup of this repo. It's really a result of a prototype. We're missing a clean way to make modular "plugins" etc and there are some other rough edges.