Enable ColorMatrixFilter function chaining

This allows, e.g.:
new ColorMatrixFilter()
    .adjustHue(h)
    .adjustSaturation(s)
    .adjustBrightness(b);
add return value to ColorMatrixFilter.concatValues
fixed that 'Texture.empty' sometimes did not return the requested size (refs #569)
Merge pull request #434 from tconkling/chainableColorMatrixFilter

Enable ColorMatrixFilter function chaining
small indentation fix