Added essential field to application base class. Wrote registry method to return non-essential apps.
PEP8 fixes.
Renamed get_non_essential_apps method. Modified null check per code review.
Merge branch 'develop' into non_essential_apps
Renamed non_essential_apps to use private modifier.
Comment fixes and style conventions.
Merge pull request #57 from jivid/non_essential_apps

Added get_non_essential_apps() method.