Add an optional bedrock mode#117

Add an optional bedrock mode to the plugin. This is super usefull for servers that run GeyserMC and allow bedrock clients. Since the difference between left and right click isn’t given in bedrock, they can choose to buy or sell. When the mode is enabled, add a GUI after clicking on the item to choose to buy or sell. This way we can provide support for bedrock users!

We encourage you to use the ShopGUIPlus SellGUI addon when it comes to supporting bedrock users.
https://www.spigotmc.org/resources/shopguiplus-sellgui.85170/