Major update to simplify and document the custom build example

Fix gimbal indicator so that angle values match the markers
Select thermal mode on thermal menu selection

Custom vehicle selector now affected by theme change. Cosnistent with other actrive elements

Drawer now affected by theme, consistent with the rest of the active elements.

TODO: Add hover for desktop

Added gimbal pitch SVGs for indoors and outdoors theme

fix to even out the toggle buttons

Custon On / Off  switch updated to show label when off. Now works more like a toggle

Custom Example: Fix gimbal state getting out of the limits. Fix palette button not working if not in thermal mode. Increase zoom buttons

Smaller border and some more distance between the circles

* Move the Multi-vehicle UI next, not under, the indicators
* Remove the icon

This is a small experiment into creating a custom theme for QGC.