Revert back to two types of presets: instruments and kits

[iurienistor]

Allow the user to create presets for individual instruments, which can be loaded into the currently selected instrument slot in the kit.

Discussion: #108

[MaZe6K]

I think it would be good if the trigger key would not be saved in the individual instrument preset, so you can replace sounds in your kit without having to adjust the trigger key.