Disable draft submission button immediately after clicking

[lberrymage]

Currently once a user clicks "Submit for review," the button remains enabled until the network request returns with success. This gives the impression of delay in the UI and allows the user to erroneously click the submit button multiple times.

Instead, the button should disable immediately after clicking (perhaps with a loading indicator to show that submission has not yet occurred), re-enabling as appropriate in the event of an error.