Bump up the default font size, use consistent font sizes

Bump up the default font size, use consistent font sizes

opac/parts/css/fonts.tt2 defines all of the font sizes we should be
using for consistency throughout the TPAC. There was a need felt to bump
up the default font size in the mobile UI from 12px to 12pt, which was
matched by a number of sites who had also bumped the normal UI up to
14px or 15px. Rather than having a weird font-size jump when you narrow
a browser window to < 600px, keep the same base font size... but bump it
up.

Also, replace hardcoded 100% etc font sizes with the templated font
sizes for consistency.

Signed-off-by: Dan Scott <dscott@laurentian.ca>