Allow pressure on pencil tool with power stroke LPE

Add pressure to pencil tool by powerstroke.

Here are a preview of the new branch running:
https://archive.org/details/inkscapepencilpressure

Please, I'm not english and there is some complex strings here:
/src/ui/dialog/inkscape-preferences.cpp
Please update it before merge.

Once is merged Based on user feedback we need to change the defauilt values in preferences to a most suitable values (I have an anciant tablet and a more modern one and both need diferent parameters for the same output)