Update CSS with even more custom rules

I think I got almost everything that's displayed.
Deprecate ModelMenu and excise references to it

Go with the ModelMenuPanel instead. Bye, hamburger menu!
Fix alignment issue with ModelMenuPanel

On Chrome, when the "open" button was selected, the highlight on left
side of the button was truncated.
Set font weight of "Model" and "Parameters" tabs

Because they're the only tabs, they're selected, and boldfaced by
default. Override to use normal weight font.