Slider/Text and Up/Down UCs: drop internal StdFont objects

Same idea as pdLabel.  Besides shaving a few dozen KB off the compiled
.exe, this also reduces dialog load time, project compile time, and live
update-against-theme time.

The only exposed font property is now a dedicated FontSize parameter.
The font name is set automatically via a new updateAgainstTheme function
(which will ultimately be used by all PD's user controls, to allow for
changing the active theme at run-time.)  Bold and italics are not
supported for these controls, by design.