Pen sensibility (toggable)

Sazdx

For users that use a tablet to make pixel art, it would be great to have a sensibility option that can be toggable (in case they don't want to use it all the time) and have that work with the pen, eraser and color replacer

GaRv3

Yeah, this is really needed - at least for opacity!
Shouldn't be too hard to implement. At least for Windows systems.