Add UX and feedback to the chat input box.

[mschnee]

The current chat box is a textarea and a submit button. The textarea is cleared when the message is sent. The input form needs the following UX ehnahcements:

• The textarea and button both should be disabled, and some kind of "pending" animation should play.
• If there is an error of some kind, there needs to be some messaging to that effect in human-readable text. The textarea and button should be un-disabled.