Added reset() function to game screen, dded removeAll() to entity manager and silencing options, allowed no background on scenes

Signed-off-by: Sam Hellawell <sshellawell@gmail.com>
Few other things

Signed-off-by: Sam Hellawell <sshellawell@gmail.com>
Merge branch 'HEAD' of https://github.com/SamHellawell/oni.git