Less player position update and smooth ai movements

[sherpal]

Currently, players send they position (and related information such as speed or rotation) to the server 60 times per second. This is way too much and will not scale well with going to ~10-15 players (this would mean 900 actions per second, only for player movements!).

This change should comme with a feature that AIs should have smoother movements, in the sense that they should not have a speed be either 0 or full speed, but should rather accelerate from and decelerate to 0 speed.