removed demo.mix
Merge pull request #4750 from Mailaender/demo-mix

Removed demo.mix
StyleCop
moved internal time step setting to Game

player should not be able change it as it is not synced yet
add a pause/slowdown/play/fastforward button for replays

closes #4633
separate World and Ui LastTickTime
use relative tick time intervals
keep the catch up for small delays and truncate larger ones