I added Sustain to MidiKeyboardState

I needed the MidiKeyboardComponent to display when the sustain pedal was pressed, which wasn't built in to the library.  So, i added it.  

you can see it in action here at the 0:06 mark.  


I've attached the code synopsis that does it, as I had to modify a few source files to do it that were part of JUCE 3.20


Jules, do you think this could be something to permanently add to the MidiKeyboardComponent class? 

It's something we should add, but probably not in this form. Since we've been beefing-up these midi keyboard/synth handling with the new MPE handling classes, that'd be the place for it, where the logic would need to be more complex than this.