Replacement code to speed up work on the map and fighting mistake 'manual control lost' when connected joystick with armed UAV

Added a signal handler to force toggle the switch. Not sure why the normal signal is not being respected.

Moved "Grid Lines" out of General Options and into the Video Stream Widget
Made a QGC custom Switch element

Clarify the title of the "Video Stream" panel (instead of just "Video")

The failure got triggered by 3c55e2b0

sincos is not used anymore, so drop the definition

Nope, it's microseconds alright. The autopilot I was testing with indeed only had 19 seconds of "armed" time.

Fix #5812
Show an error message when creating a KML without 2 items at least
Signed-off-by: Patrick José Pereira <patrickelectric@gmail.com>