Wheelchairs

Implemented teleporting using an ender pearl or other methods not causing you to dismount when riding a wheelchair.

Added the Gliding upgrade, applied using an elytra. This upgrade allows the chair to jump freely, and enter a flying state if a jump is performed whilst in midair. The rider may even use firework rockets to boost!

Note: There is a marked drop in velocity when beginning to fly, but unfortunately that's pretty much unavoidable with how Minecraft handles mount steering. However, I don't foresee this being a major impediment, given the abundant use of firework rockets in standard gameplay.

Added a dismount locking feature. Using a keybind, players may prevent themselves from dismounting any vehicle or mount when sneaking. Among other things this allows wheelchair users to shift+rclick things, as well as to avoid falling off of edges.

Added visuals for all upgrades, as well as sounds for most meaningful state changes.