Add default CSS style for mouse position

Missing CSS was confirmed with issue #680, this commit is to fix it and change
ol-mouse-position class to ol-mouseposition. I choose for the moment the top
right corner to display the coordinates from mouse position control because of
potential conflict with the scaleline control.

src/ol/control/mousepositioncontrol.js

@@ -28,7 +28,7 @@ ol.control.MousePosition = function(opt_options) {
   var options = goog.isDef(opt_options) ? opt_options : {};
 
   var element = goog.dom.createDom(goog.dom.TagName.DIV, {
-    'class': 'ol-mouse-position'
+    'class': 'ol-mouseposition'
   });
 
   goog.base(this, {