Remove box-sizing trick from palaso-ui.css

The box-sizing trick is highly useful when designing new CSS, as it
simplifies your layout immensely... but the ScriptureForge template was
designed by someone who didn't know about (or chose not to use) the
box-sizing trick, so it changes the ScriptureForge layout in ugly-ish
ways. So we'll remove it from palaso-ui.css, and put it only into
layouts that were designed from scratch for it.