Added a config option for excluding files from being backed up

[broskisworld]

This is a relatively small change that adds an additional config option mscs-backup-excluded-files in mscs.defaults (optionally mscs.properties) for excluding files and directories from being backed up.

I'd imagine the primary use for this would be for games with map plugins, though it could also be used for anything in the world folder. Even with differential backups, servers with overviewer or dynmap can make for extremely large backups, despite the fact the fact that tilemap renders can be re-generated from the world file itself in the event of a server crash.

This additional config allows admins higher control over exactly how much space they want to use for backups and enables admins with smaller hard drives to still keep limited backups of critical user data.

The property accepts an individual item or a comma-separated list, and evaluates$WORLD_NAME to the name of the world being backed up. I've added a few example use cases below:

• mscs-backup-excluded-files=plugins/dynmap/web/tiles excludes dynmap tiles only
• mscs-backup-excluded-files=plugins/dynmap,$WORLD_NAME_nether,$WORLD_NAME_the_end excludes the entire dynmap configuration, as well as the nether and the end world files
• mscs-backup-excluded-files= default configuration (keep everything)

[sandain]

This PR looks good, thanks for the patches. I see how this could be useful.