Configurable Gesture Control

[ems316]

Is your feature request related to a problem? Please describe.
I would like to have control over the behavior of the longpress gesture.

Describe the solution you'd like
Instead of sending a right button down event to my vnc server, I would like to send a left button down event so that longpress is a hold on my vnc server rather than a right click.

noVNC/core/rfb.js

Lines 1282 to 1285 in ed1fef4

	case 'longpress':
	this._fakeMouseMove(ev, pos.x, pos.y);
	this._handleMouseButton(pos.x, pos.y, true, 0x4);
	break;

I think it would be beneficial to have an option that allows a user to configure the behavior of the longpress gesture. The suggested feature might add a flag in this location that either sends the bitmask 0x1 (longpress as hold) or bitmask 0x4 (longpress as right click) depending on how the flag is set.

Describe alternatives you've considered
N/A

Additional context
#417 considers using a gui element to configure this functionality. I would just like to be able to configure it via a cli option.