Created sprayNumber2 Added Point and Stroke class

Getting ready to implement point extrapolation and proper object
oriented stroke management.
Refactoring
Proper object structure + filling in the gaps
Added texture based distribution of the particles

First test (see "radialGradient4")
Adjusted gradient lookup
Added debug option
Don't compute/redraw all points on every frame
Better image-gradient-based brush handling
sprayNumber3 functional with gradient based dispersion
Merge pull request #19 from SableRaf/master

Faster spray simulation + image based dispersion