Making default options modifiable

Storing default options in global object, so that any one can access or modify it easily using jQuery's "$.extend()" method as below :

$.extend($.fn.datetimepicker.defaults, {
       format : "d/m/Y h:i A",
       ....
})

So we don't have to set the same options again and again, it will automatically get reflected to all the newly created datetimepicker objects.