Note: is actuator the right term?

* Four default actuators for changing paintop options:

    - wheel
    - pressure, pressure + shift
    - tilt, tilt  + shift
    - rotation, rotation + shift
    - shortcut keys

All options can be associated with one or more actuators. An actuator
type can be assocatied with one or more options.

Options need to reimplement actuate() to change their value according
to the value of the acuator, for instance for brush size.

Or they check whether an actuator is activated when called from the
paintop (like for pressure size, pressure opacity or pressure darken).

There are two kinds of actuators: permanent and transient. Transient
actuators do not change a setting, but are applied during the paintop 
option's apply method (if there's one)

Two methods: actuate (change setting permanently), apply (change setting
while painting, transiently)

Path:

From canvas to paintop box to options:

wheel
pressure, rotation, rate, tilt + shift
shortcuts

Implementation: Kis(Q|OpenGL)Canvas calls an emit on KisCanvas2 that is
connected to KisPaintOpBox; KisPaintOpBox calls actuate on KisPaintOpPreset,
which is responsible for actuating all options.


From paintop to option (transient)
pressure, rotation, rate, tilt, (mouse speed, as in cpaint?)

Implementation: as currently

