Responsive masthead

This is a series of changes (collapsible into one if you want!) that develop a responsive approach to the Tropospherical masthead. The idea is:

* Log in is now a button in the top masthead that when clicked does a JavaScript modal window with the login screen.  If JS is off, it clicks through to the routine login page.
* When the screen gets too small for account links, have the user icon in the top right of the masthead.  Additionally, have the username on the left side of the menu bar--clicking on this activates a JavaScript modal that has all the account links and the logout button on it.

Left to do:

* Ensure this works with Celerity, Gradation Horizontal, Gradation Vertical
* Right now account link modal activation doesn't have a fall back--should make an account links page it ends up on instead.