edit: Implement editing bars on ships and land units

edit: Implement editing bars on ships and land units

The edit command doesn't support editing bars on ships and land units.
Has always been that way.  The stock game's ships have always been
unable to load bars.  Not the case for land units.

Unfortunately, the obvious key 'b' for bars was burned on plague time
in 4.0.17.  Use key 'B' instead.

Signed-off-by: Markus Armbruster <armbru@pond.sub.org>