Fix RadioButton group problems. Rework RTL settings to match correct usage.

Fix RadioButton group problems

Survey And Corridor now share same transect generation code. Better unit tests for both with more coverage.

Force consistent setting for offline vehicle

Use only default values when running unit tests

Visual tweaks for mission items

Cherry pick from master

Better error message

Add note about ADSB server settings

Correct handling of terrain ready when loading back from file

More changes to ArduPilot manifest lookup

Unit Test for Survey command sequence generation

Major rewrite of Survey generation for simplicity. Also includes support for CONDITION_GATE.

Temporary use setting for using CONDITION_GATE in Patterns

Unit test for mission transfer error string checking

Much better error reporting for Mission transfer errors

Plan: Add support for takeoff item required

Handle multiple file extensions correctly