Updates to CSS rules for menuButton in ComponentCell
Update to CSS rules for menu items in ComponentSelectionMenu
Match fonts used in ComponentCell menus
Make ModelMenu look like a MenuBar

The problem is that MenuBars don't justify MenuItems correctly at the
right edge of the browser window, where the ModelMenu appears. The
ModelMenu is a PopupPanel, but with a CSS box-shadow, which makes it
look like a menuBar.
Apply styles to ModelMenu items

This also removes a hardcoded value from the ModelMenu!