Made convolution filters tweenable.

Unsharp mask, soft blur, sharpen, emboss, edge detect are now "tweenable";
however, I think I need to tweak the convolution matricies. At 0 there
should be no effect applied which corresponds to a matrix with just a
`1` in the middle (ie [...1...]). If the `filterAmount` is small then
the matrix is all near 0's causing the image to 'flash black'. If I always
add a 1 in the middle then the images become too bright...