confusing with 3 bool settings (in the sbbsecho.ini) to represent 4 valid
security requirement levels, so I attempted to simply the menu options to
make it easy for sysops.
BinkpAllowPlainText now defaults to true since the supported encryption method
isn't even an official FidoNet standard, yet.
I also added/updated some online help (F1) help text.
Added an "Exiting" popup (like SCFG) when exiting.