Update to a later Java version

[A248]

#499 raised the point that HSQLDB 2.6.0 requires Java 11. If AdvancedBan remains on Java 8, it will have to be content with staying on the 2.5.x versions of HSQLDB. They're supported for the moment, but it's not clear for how long libraries will continue to support Java 8. Caffeine is another example of a library with a Java 11 baseline.

With the 1.17 update, 1.17 servers will be forced to run Java 16. I think moving all the way to Java 16 is a little extreme and quite disruptive, so I don't suggest that for AdvancedBan. A move to Java 11 would be a reasonable compromise, however, and it could freshen up the codebase somewhat.

[DevLeoko]

I don't think this is a good idea yet as 50%+ of our users still use Java 8