Change Instrument Materials
Added new configuration option which lets you change the materials for the different instruments (e.g. for the bass guitar, another type of wood can be used). Please note that some instruments only work with only one type of material. Please refer to the Minecraft Wiki for all the possible materials.

For the different material names used in the configuration, please refer to the Bukkit Material enum for your server's respective version.

Other smaller changes
✓ Added support for 1.13.x
✓ Added /noteblockeditor reload command for reloading the config
✓ Added bStats for plugin metrics