Fix the hangup on Linux when the LUT docker is present

This patch does two things:
1) Fixes LUT docker to update configuration only when some LUT-related
   config options really changed.
2) Adds a safe barrier locking in KisCanvas2::setDisplayFilter and
   KisCanvas2::setMonitorProfile. This is done using a new class
   KisDeferredSignal, which is based on boost::function + boost::bind.

TODO:
There is a still a "bug" that on every change of the settings (LUT-related
settings) the docker calls setMonitorProfile() four times! Well, it doesn't
lead to any problems right now, but this is surely no good.

BUG:313218