gcs input widget: fix flightmode position calculation

Range was effectively being computed/split across 0..N-2 and
would only ever show N-1 (ie. the max flight mode) when
valueScaled was exactly 1.0f.  Even the slightest jitter on the
flightmode channel would result in the GUI drawing the flight mode
as N-2.

The code in the GCS now matches the code in the flight firmware.
GCS Config: if no board then have default max rate

In the case of a flaky connection it is possible to connect to
the FC but not get an update of FirmwareIAPObj in which case no
valid board plugin is found. This was causing a crash but we
should handle this more gracefully.
GCS:Added target url to modules help button

Fixes #1046
Airspeed: move ADC setting to airspeed settings

Allows us to remove the ADCRouting object which is
just confusing and mangles concepts.
Battery: move ADC settings to FlightBatterySettings

Get rid of ADC routing layer
UAVObjects: remove ADC routing object

It was a weird concept and is better moved to specific
setting objects instead of spreading it around.
Modules: add the battery ADC pin to UI
Modules: add ADC to airspeed UI
FlightBatterySettings: enable current and voltage pins by default

This is the most common configuration by far if people enable the
Battery module so use sensible defaults.
FlightBatterySettings: more reasonable default scales

Using default values for AttoPilot 90A sensor to pick something
in the middle, but most people will have to adjust this. But 1
is a very far off value.