Fetch user data asynchronously

[pbrisbin]

• Make all calls to getUser asynchronous
• Fire the first attempt right when Carnival loads
• Expect Carnival.user to be present when the form is rendered, if not launch the login window

Resolves #170, #248

[jferris]

Do we need to fire a request right when the script loads? That will increase the load on the server pretty dramatically, as most requests won't involve making comments.

[pbrisbin]

Do you think moving it to when/if the sidebar is opened will help enough (assuming it works)? That would still be more than is strictly required.

[pbrisbin]

Seems to still work moving it there. I could get close, but never quick enough to trigger an unnecessary login.

[jferris]

Looks good to me.