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.
/instrumentation/FG1000/adc-update-frequency can optionally
be set to control the update frequency of the main ADC information.
Set to "0" to update every frame.
ConfigStore for storing and retrieving config settings (needs XML import/export)
Header display with 4 different header fields (all configurable)
Publisher for ADC and FMS.