Adds a button to the map
Simple button:
Only shows the zoom level, do zoomin when is activated and restore zoom when is deactivate:
activate: function(){
alert ('Active!!\nThe map has ' +map.zoom + ' zoom level');
map.setCenter(new OpenLayers.LonLat(lon, lat), map.zoom + 1);
},
deactivate: function(){
alert('Do the zoom to '+zoom+ ' level!');
map.setCenter(new OpenLayers.LonLat(lon, lat), zoom);
}