Add AdvancedPImage Convolution

Convolution is now a method within AdvancedPImage.
A Kernel (2D float array) can be used to convolve an
image

Used convolution and a sobel kernel to create
gradient images in X and Y
Refactor Kernel For Easier Use

Having the backwards array (data(y)(x)) made access confusing
but creation easy. Access has now been delegated to an
easy get(x,y) method that does the reverse behind the scenes
Remove AdvancedPImage PApplet Implicits

The implicit is now in the constructor, allowing anything
extending or mixed-in with an AdvancedPImage to use
the applet