move stuff into success callback

now, since we're communicating with the server here, we have to wait for the action to finish, before we change something on the UI. 
This is described in [Backbone.Model#save](http://documentcloud.github.io/backbone/#Model-save), the callback function stored with 'success' will be executed after the server responded with a 200 (success) Status code.
If the code would be as it is without this patch, it would always be executed, even if the server would respond with an error.

(I know, you removed the success function before, because it was empty. but at that point it wasn't sure if something would go into there or not.)