Elytra Boost (Soar)

This is an expansion and optimization of the original mod by dragon_evol.

Features:

- Use W / S (Forward / Backward) to acclerate / decelerate smoothly during flight.

   Configurable maximal speed and accleration / deceleration strength.

   Sprinting in air to be faster.

- Use R (Default) to start / end elytra flying. (make takeoff and landing easier)

- Client can turn ignoreServer on to use local config. (i.e. speed settings etc.)

   Server can turn serverOverride on to override client config. (even client set ignoreServer to true)

- Motion calctulation is now done on client side, improving performance when network is bad.