Changed how new/updated/validated entries are exported:

Rather than a single "last_export" date/time stored in the <syncdata>.ini
file, each entry in the database has its own "exported.on" date. This allows
the 'sbbslist.js export' event to run frequently, but not export *all* updated/
validated entries every time. The default export frequency is every 7 days
(weekly), but this can be adjusted via modopts.ini [sbbslist] -> export_freq.
This should help reduce the chatter in the SYNCDATA conference/echo
but still allow newly-created entries to be exported quickly.

On the down-side, you cant' effectively export to multiple message bases.
But I don't think anyone is doing that, so it's probably a non-issue.

Also:
- Beautified the format and sort field selections a bit
- Disable Ctrl-P processing in the BBS (now used for PgUp) rather than Ctrl-U