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.

css/ol.css

@@ -81,6 +81,13 @@ a.ol-full-screen-true:after {
   display: inline;
   list-style: none;
 }
+
+.ol-mouseposition {
+  top: 8px;
+  right: 8px;
+  position: absolute;  
+}
+
 .ol-scale-line {
   background: rgba(0,60,136,0.3);
   border-radius: 4px;