PRs merged

This update has merged a lot of pending PRs with new features and bugfixes and hopefully fixed some critical bugs with items.

Warning

The contains condition was severely changed in this update, please take a look at its new patterns and report any issues you might have with it.

Here's the changelog;

• Added zombie horse alias for undead horses (thanks to @Wealthyturtle, closes #1389).
• Added experience level up/down event.
• Added the ability to parse entities by UUID (thanks to @ShaneBeee, closes #1352).
• Added the ability to modify a player's view distance (requires Paper, thanks to @ShaneBeee, closes #2010).
• Added an expression to get a portal blocks in a portal create event (thanks to @Wealthyturtle, closes #576).
• Added head alias to the skull expression (thanks to @Wealthyturtle).
• Added an effect to cancel dropping of inventory/experience in some events (thanks to @Blueyescat).
• Added an expression for getting and setting the entity type of a spawner (thanks to @Wealthyturtle, closes #1186 and #2385).
• Improved the command with cooldown example script (thanks to @bluelhf).
• Reworked the contains condition (thanks to @Blueyescat, closes #1404, #1838, #2122).
• Fixed some grammatical errors in the documentation (thanks to @noftaly).
• Fixed removal of items from inventories (Closes #2446).
• Fixed issue where clicking outside an inventory would throw a NPE (thanks to @Wealthyturtle, closes #2306).
• Fixed issue with sound effect throwing an exception when the input was invalid (thanks to @Wealthyturtle, closes #2412).
• Fixed displaying issue with cats and pandas (thanks to @Wealthyturtle, closes #2440).
• Fixed quit event being cancellable (closes #2444).