Different cooldowns based on permission groups

[percyqaz]

Got a feature requested on Spigot forums Spryzeen:

could have per-group cooldown and warmup, basically will allow us to make custom cooldowns for each rank

I've not worked with permissions in a plugin before, and this is a step beyond normal permissions because usually a permission is just a 'yes-or-no can you use this feature', but this would be different numbers depending on the player

Will have to do some reading on if this is possible, and if I can release a version of the plugin that works both with permission groups or carries on as normal if they aren't set up