change hold delay

[forresto]

With PointerGestures I monkeypatched a config for HOLD_DELAY and other options googlearchive/PointerGestures#17 ... would be nice if those were exposed options here.

PolymerGestures.dispatcher.gestures.forEach( function (gesture) {
  // hold
  if (gesture.HOLD_DELAY) {
    gesture.HOLD_DELAY = 500;
  }
  // track
  if (gesture.WIGGLE_THRESHOLD) {
    gesture.WIGGLE_THRESHOLD = 8;
  }
});