Add web app manifest

[Nockm]

https://developers.google.com/web/fundamentals/web-app-manifest

[electronstudio]

I added one, combining all the elements recommended by a couple of different online generators. Have not tested it at all so you should probably have a look.

[electronstudio]

So it seems ok, but Chrome still doesnt consider us a 'proper' web app because we dont have a service worker because we dont have HTTPS. I think the best we can do it pop up a reminder to tell user to add us to homescreen.

[Nockm]

A popup can be shown via:

MobControlJava/src/main/resources/client/lib/logger.js

Lines 24 to 27 in 352007b

	Logger.prototype.setNotification = function setNotification(text) {
	this.notificationElement.innerHTML = text;
	this.notificationElement.style.display = text ? 'block' : 'none';
	};

Although it might not be ready yet, as we probably want a button to dismiss the notification which hasn't been implemented yet.