Work on facebook login functionality.

In particular, make a basic login function that is now linked to a
default button in the modal pane (this pane doesn't yet disappear
after successful login btw). Successful login (which is also checked
for in the asynchronous sdk load) sets a global user name variable and
sets the "logged in as" field to visible so that the logged in as ___
now displays in a meaningful way.

Still kludgy.