Bug 588405 - Handle status menu button appearance in JavaScript

Bug 588405 - Handle status menu button appearance in JavaScript

Make the ClutterText and ClutterTexture from the status menu
button available to JavaScript, and from there improve the
font definition of the user name.

shell-status-menu.[ch]: Add public get_name() and get_icon()
    functions that return the user name label and icon
    texture, remove the markup from update_name_text().
panel.js: Set the font for the button consistently with that
    of the other panel labels.