Camera: add config option to disable snapshots during videos

patchset2:
- disable snapshot welcome message as well
- disable jpeg quality settings

patchset3:
- minor correction

Change-Id: I5f6e14f1125a9d47e03bb35fdc4ff358c589b73e
Signed-off-by: scott <scott@ubuntu.com>

Conflicts:
	res/values/config.xml
Fixes back button in Video Camera as per this bug: https://slimtrac.slimroms.net/redmine/issues/484

Change-Id: I688f3137481f2e5a9cdbc379db8d96c47bf8ddc4