Add categories within the tx form

While adding a category currently doesn't abort the transaction form, the category listing isn't updated if the user happens to add a category. I can think of three ways to do this:
1. provide a text input inside the transaction form that accepts the new category(ies) to be created
2. add a refresh button to the category listing, which will re-populate it
3. pop up the new category form using JS and reload (so it's somewhere between 1 and 2)