The G1000 highlights the active NAV and COM radios in cyan.
In the NAV case, this is the radio being used by the CDI.
In the COM case, this is the COM radio selected on the audio panel.
Add Multikey support for the FG1000 (:GF and :GP) to improve useability
by allowing direct entry of strings. This is massively easier than
fiddling with the control knobs.
Also correct interface variable name "frequency" to "period", which is
more accurate.