ENYO-99: Implement double-tap support

### Issue:
We don't have double tap support in Enyo (and generally don't think double-tap is a good UX pattern), but Garnet UX requires it for W2.
Needs to be implemented purely at JavaScript level (no WebKit support).
### Fix:
Before sending a tap event, check for doubleTapEnabled. If yes, set a Timeout. If another tap comes before timeout expires, send a double tap event. If timeout fires, send a tap event

Enyo-DCO-1.1-Signed-off-by: Krishna Rangarajan <krishna.rangarajan@lge.com>