Count down the band change timer in the status bar

SOBandChangeTimerDuration and MOBandChangeTimerDuration say how long a
station has to stay on a band it has just moved to. Both were read by
nothing: N1MM counts them down in its info window, which this program
does not have.

The countdown now stands in the entry window's status bar, next to the
contacts and multipliers, ticking with the clock that is already there.
BandChangeRules.StayLeft works it out from the log, starting the stay at
the minute after the contact that changed band, which is where N1MM
starts it.

Which contests show it is decided at runtime rather than by a list: the
rules come from the contest for the entry's own category, so a file that
asks for no stay, or asks for one only of single-op entries while the
station is entered multi-op, shows nothing at all.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RoGtneMQaz4M9w7Kk49AVD

docs/unfinished.md

@@ -111,9 +111,7 @@ with the CW and SSB running of the contest.
 `.udc` settings that are still passed over. `MultiplierBands` and
 `QsoErrorString`, which are about the windows rather than the score.
 `GenericPrintString`, which is the layout of a printed log rather than a
-Cabrillo one. `SOBandChangeTimerDuration` and `MOBandChangeTimerDuration`, the
-minutes a station has to stay on a new band, which N1MM shows as a countdown in
-its info window; this program has no info window and no countdown.
+Cabrillo one.
 
 `MultWindowType` is read as far as the score goes: it names the list a section
 multiplier is checked against. Four of N1MM's lists are held here — the ARRL