overhaul the whole ruleset

I have explicitly listed Sniffs coming from Squiz, PSR2 or Generic so we
can easily enable them later on.

This is still highly experimental, we probably to remove more checks to
avoid spaming the submitters with changes we do not really want to
enforce for now.

Change-Id: I758ddc424b45d2408f4831564e9881d3bab489e9