ACU motion fixes and "named-positions" feature

[mhasself]

Description

• When the "go_to" task runs, and Sun avoidance is enabled, and the platform is already at the target position, there is a risk that the sun safety check will crash, because of the trivial trajectory. This is now fixed.
• The ACU's ProgramTrack mode will reject points that specify el speeds that exceed the platform limit, even if there is no actual motion in elevation. This caused confusion during testing, so now el_speed is set to 0 in the ProgramTrack data no matter what the user says.
• A new task, "go_to_named" will cause the platform to go_to a target az, el position that has been configured through the command line. This is mostly to support ocs-web widgets ("go to Home" button) but has other applications, where a script could be written that is general but for which the "home" position is different per-platform.

Motivation and Context

Deals with #601 and ground work for ocs-web:52.

Resolves #601.
Resolves #565.

How Has This Been Tested?

Tested all on SATP3.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[mhasself]

(Just added fixes to address #565 as well.)

[BrianJKoopman]

Looks good to me!