Add option to display short dates in verbal/unambiguous formats

Although we've added (in SBBS v3.20) configurable numeric date input/display
formats for the system, the output was still ambiguous for users (e.g.
NN/NN/NN which could be interpretted a number of ways), so I've added an option
to choose "verbal" short date formats to be displayed where possible instead.
The same value separate from the numeric format (whatever the sysop chose) is
used in the verbal date output, but since month name abbreviations are 3
characters, only one separator is used (to keep the output length fixed at 8
characters).

The new "Verbal" short date display format is choosable in the SCFG wizard and
via SCFG->System->Short Date Format.