Allow application developers to modify cursors

With this change, cursors can be set on the map target again.

css/ol.css

@@ -159,12 +159,8 @@ a.ol-full-screen-true:after {
   -ms-user-select: none;
   user-select: none;
   -webkit-tap-highlight-color: rgba(0,0,0,0);
+}
 
-  cursor: default;
-}
-.ol-viewport .ol-unselectable:not([ie8andbelow]) {
-  cursor: auto;
-}
 .ol-zoom {
   position: absolute;
   top: 8px;