Show that modals are doing something when they are submitted

[alastair]

At the moment when you submit a modal it's not clear that it's actually doing anything until the response comes back. This means that the user could get confused and click the button again, or think that nothing is happening.

It might be a good idea to show to the user that something is happening. Some options:

• make the submit button disabled and change the shade of it
• make the whole modal fainter and disabled?
• Show a spinner in the button or in a corner of the modal to show that something is happening