Use CustomSizedInvMenu but don't need to install UIResourcePack

[ClickedTran]

Dear Muqsit, I'm ClickedTran, I'm from Vietnam, I've been a fan since I first started coding at PocketMine-MP, today I mustered up the courage to create this 'pull request' with the hope of he will approve it

WHAT IS NEW IN IT COMPARED TO THE ORIGINAL? Sir, I have integrated InventoryUIResourcePack into your plugin, but it has been renamed to CustomSizedInvMenu Pack but sir, I am sure it is no different from the original InventoryUIResourcePack, hope you can agree to this pull request, you can create a new branch for it if you want. Thank you for reading this small request Written by: ClickedTran