Megapixels profile

This is the initial profile for megapixels, it confines as much as possible but leaves the postprocessing scripts unconfined since those are supposed to be user adjustable.

I also add an allow-some-applications abstraction that allows common apps to be launched. It's inspired by https://github.com/nibags/apparmor-profiles/blob/master/apparmor.d/abstractions/open-some-applications and the purpose is allowing applications to be launched as helper of the current process. These apps should definetly have profiles added but those don't exist yet.

See #1