New Added client-side Sentry logging

Using Raven.js allows logging client-side javascript errors to the
configured Sentry server.

htdocs/includes/raven-js/example/file2.js

@@ -0,0 +1,12 @@
+function multiply(a, b) {
+	"use strict";
+	return a * b;
+}
+function divide(a, b) {
+	"use strict";
+	try {
+		return multiply(add(a, b), a, b) / c;
+	} catch (e) {
+		Raven.captureException(e);
+	}
+}