Some changes & updates

When you have many instances of BlitzMap the overlays from all instances are put together in mapOverlays array. I created a function replaceOverlays() to replace mapOverlays array with array of overlays from single map. Its useful when you want to get overlays from one map. I use it in forum when first instance is executed in topic and second instance is executed in reply form.

`First instance`
BlitzMap.setMap('map_canvas1',false,'mapData1'); // map not editable
`Second`
BlitzMap.setMap('map_canvas2',true,'mapData2'); // map editable

`Ajax call`
$.ajax({
beforeSend:function(){
BlitzMap.replaceOverlays( 'map_canvas2' );
BlitzMap.toJSONString();
}
});