Factor out MatrixClient methods to MatrixBaseApis

Starts work on a class which is intended to just wrap the Matrix apis with very
simple functions.

There is a lot more work to be done here. For now, I have just taken methods
which don't refer to anything in MatrixClient except _http. This excludes a
bunch of things which refer to $userId, as well as the login stuff because of
the deviceId stuff I've just added :/.

For now, it's an internal class. I don't really see any reason it can't be
exposed to applications, though.

lib/utils.js

@@ -332,6 +332,30 @@ var deepCompare = module.exports.deepCompare = function(x, y) {
     return true;
 };
 
+/**
+ * Copy properties from one object to another.
+ *
+ * All enumerable properties, included inherited ones, are copied.
+ *
+ * @param {Object} target  The object that will receive new properties
+ * @param {...Object} source  Objects from which to copy properties
+ *
+ * @return {Object} target
+ */
+module.exports.extend = function() {
+    var target = arguments[0] || {};
+    // disable jshint "The body of a for in should be wrapped in an if
+    // statement"
+    /* jshint -W089 */
+    for (var i = 1; i < arguments.length; i++) {
+        var source = arguments[i];
+        for (var propName in source) {
+            target[propName] = source[propName];
+        }
+    }
+    /* jshint +W089 */
+    return target;
+};
 
 /**
  * Run polyfills to add Array.map and Array.filter if they are missing.