WinGui: Fix AllowSleep option. Port the Numeric Stepper control from Vidcoder onto the Picture settings panel. This should fix a number of strange behavioural issues with the old control. Please report any new issues that this causes.

git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@5158 b64f7644-9d1e-0410-96f1-a4d463321fa5