avconv & Start Time support

Basic avconv support added for remuxing video.
UTC Start Time support added by mattlapine.
Merge branch 'avconv'

Conflicts:
	.gitignore
Refactoring
Re-adding AVCONV work.
Adding avconv & flags
Merging
Cleanup & minor fixes.
Fixed mythcommflag.
Merge branch 'master' into avconv

Conflicts:
	mythEx.py