UltimateMobCoins

Changes:

• Allow negating permission to prevent players with the permission to purchase an item.
• Should fix error when reloading plugin while players have a shop opened.
• Fixed grammar issue in pay_sender message.
• Should fix error that can happen when using itemsadder item.
• Added support for libreforge in the plugin because it takes too long for the PR to be accepted into libreforge itself.
• Added leaderboard placeholders to placeholderapi and miniplaceholders expansion.
• A lot of code improvements.