3.6.0 -> Language presets & Hotbar selection syncing

This update brings 2 new requested features:

1. Language presets. We thrown out a single message.yml file and moved all translations to the lang/ folder.
Pre translated languages are: German (de-de), English (en-us), Chinese (zh-cn)
Thanks again to xucy for providing the Chinese translation and the idea

2. Another requested feature by our own private server community was another sync module: Hotbar selection syncing
It is now possible by enabling the sync.selected_hotbar_slot to sync the Selected Hotbar slot. It makes much sense to use this
in combination with the inventory sync module, making player's live easier.