node-singleton implementation to release the usb listening

[gre]

need to reboot this idea

ledgerjs/packages/hw-transport-node-hid-singleton/src/listenDevices.js

Lines 26 to 41 in 0453b2b

	// stopMonitoring is causing trouble so not using that implem for now
	let totalMonitor = 0;
	const monitor = () => {
	if (totalMonitor === 0) {
	log("usb-detection", "startMonitoring");
	usbDetect.startMonitoring();
	}
	totalMonitor++;
	return () => {
	totalMonitor--;
	if (totalMonitor === 0) {
	log("usb-detection", "stopMonitoring");
	usbDetect.stopMonitoring();
	}
	};
	};

because without doing stopMonitoring(), you will have a node thread never ending.

[gre]

putting back that code creates bad seg fault because of MadLittleMods/node-usb-detection#57

another idea will be to process.on("exit", () => usbDetect.stopMonitoring())