Make ofxLEDsAbstraction resize() and render() functions virtual
Give public access to DataStart/PixelsStart/PixelsEnd/DataEnd constants in ofxLEDsFrame (should not be written by other classes)
Added overloaded resize() functions to ofxLEDsLPD8806Frame to allow custom latch data (for both prefix and suffix latches); default implementation sends the usual 32-bit zero data