Add experimental keyboard shortcut widget

It’s not cool that we have to use a separate keyboard widget for each
keyboard shortcut.

Fixes #386

core/modules/utils/dom/keyboard.js

@@ -0,0 +1,60 @@
+/*\
+title: $:/core/modules/utils/dom/keyboard.js
+type: application/javascript
+module-type: utils
+
+Keyboard utilities
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+var namedKeys = {
+	"backspace": 8,
+	"tab": 9,
+	"enter": 13,
+	"escape": 27
+};
+
+/*
+Parses a key descriptor into the structure:
+{
+	keyCode: numeric keycode
+	shiftKey: boolean
+	altKey: boolean
+	ctrlKey: boolean
+}
+Key descriptors have the following format:
+	ctrl+enter
+	ctrl+A
+*/
+exports.parseKeyDescriptor = function(keyDescriptor) {
+	var components = keyDescriptor.split("+"),
+		info = {
+			keyCode: 0,
+			shiftKey: false,
+			altKey: false,
+			ctrlKey: false
+		};
+	for(var t=0; t<components.length; t++) {
+		var s = components[t].toLowerCase();
+		// Look for modifier keys
+		if(s === "ctrl") {
+			info.ctrlKey = true;
+		} else if(s === "shift") {
+			info.shiftKey = true;
+		} else if(s === "alt") {
+			info.altKey = true;
+		}
+		// Replace named keys with their code
+		if(namedKeys[s]) {
+			info.keyCode = namedKeys[s];
+		}
+	}
+	return info;
+};
+
+})();