Fix setup flow from master to create server groups

[TheMeinerLP]

On setup flow for server groups on the master is something wrong. If in console typed on the backend question, "MASTER". Only the Global-template get the master backend property, but not the default template

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[GiantTreeLP]

Apparently this overwrites the templates every time:

https://github.com/CloudNetService/CloudNet/blob/8a225fb6cba21d288d420968fc228ea6cde5d720/cloudnet-lib/src/main/java/de/dytanic/cloudnet/lib/server/ServerGroup.java#L87-L91

This is fixed in the next release.