This resolves issues when multiple listeners try to handle the same
events e.g. for group support which would've passed it onto the normal
listeners leading to errors
Also add tax bypass permissions (#204, ChestShop.notax.buy/sell). When buying with that permission the buyer does not have to pay the tax (the seller will still get the reduced amount), when selling the seller will get the full amount instead of one lowered by the tax.
The permissions of the shop owner play no role due to there not being a good way of checking offline player permissions and it being a bit non-obvious for the buying/selling player if a shop would be with or without tax. This way all that gets changed is the amount the player pays/receives and not the shop owner (and the player should know their permissions/rank already)
The transfer event was necessary in order to correctly resolve who triggered the transaction. Economy adapters are now required to implement a listener for each of the events. It's also recommended that economy adapters that support transfers directly use that instead of passing it through subtract and add with the processTransfer method.
