widget: course indicator

[ES-Alexander]

Problem to solve

Attitude (the direction the vehicle is pointing) is not always well-aligned with course (the direction of motion), due to momentum, imbalanced thrust (for improved sensor data, or due to motor damage), and external forces from the environment (such as currents).

Currently we only have dedicated widgets for attitude, which means course corrections can be unintuitive to perform, and we're missing a useful source of information about unexpected forces acting on or from the vehicle (e.g. as a guide to lateral currents, or a notifier that a thruster is performing poorly) unless we add individual course indicators using very generic indicator mini-widgets.

Desired approach

Course is often most useful in comparison to attitude or a motion path, so ideally the course could be displayed as part of the existing attitude widgets (perhaps in conjunction with target displays (per #1280)), and on the map widget as part of showing the vehicle's motion (related to #1350), although the path trail may make a map indicator somewhat redundant.

Failing that, it could still be useful to have yaw and/or roll/pitch widgets dedicated to displaying course.

Additional context

Issue brought up in this thread

Prerequisites

• I have checked to make sure that a similar request has not already been filed or fixed.