Add distance/speed/time display to GNC255

[tigert]

This might be a bit handful, so perhaps for a bit later or if someone is looking for a rabbit hole to dig into :-)

• Add boolean flag for DST display on/off setting
• Add DME station ID
• Add DME station bearing
• Add station to/from flag
• Add DME distance (and show the whole d/s/t thing when <200nm out)
• Add DME groundspeed
• Add DME time to station string (H:MM)