Transition is not part of State class anymore

It is a function in the base module now.
Forbid explicit state setting
Update the docs
Rework transition
Use wraps() for @transitioned methods
Fix minor problems detected by pyflakes
Refactor motors base

Remote ContinuousMixin and make PositionMixin private
Refactor dummy motors
Incorporate hard-limit in motors base
Make dummy motors and tests hard-limit compliant