Support for multiple worlds

[Kryolisc]

I've implemented support for multiple worlds as I needed that for a server I maintain. Maybe this would be interesting for somebody else.

This PR restructures the config a bit, so worlds can be added to a list, allowing for per-world config:

worlds:
  world:
    # ...
    update_rate: 80
    # ...
    force_daylightcycle_false: true

worlds:
  <worldName1>:
    ...
  <worldName2>:
    ...

Another thing I had to change is the UpdateTimeHandler. It can now be used as a regular object, so multiple instances can be created and run.
Because other worlds besides the "world" are being loaded at some point later in the startup process, the UpdateTimeHandler instances will not be started at plugin load, but instead when the server is done loading. This should ensure that all worlds are loaded and can be found by the plugin.
This version works fine on the before mentioned server (Paper 1.19), but I wasn't able to do extensive testing for other versions.

That said, I also updated the Paper dependency for 1.19 and added the api-version property to plugins.yml, but that should hardly even matter, as the plugin doesn't really use version-specific APIs.

[EdouardCourty]

Hi, sorry for not replying earlier, this project was kind of on hold.

I've changed a few things, as well as I've added support for timezone.

If you'd be okay with rebasing your PR, I'd be happy to implement your changes after review!

Thanks a lot for contributing <3

[EdouardCourty]

I'll try to rebase it myself, it doesn't seem too crazy :)