core3: event framework adjusted for global Qubes object

From now, global events are emitted by qubes.Qubes object and handlers are registered there.
core3: basic global events and their documentation
Merge branch 'core3' of git://git.qubes-os.org/woju/core-admin into core3
Inital .pylint configuration file
Intial commit of Qubes doc theme using semantic-ui