UI: split ship movement module into helper mixins

Tests also split accordingly. No functional changes.
Includes small fix to a few test include paths.
Add utility to plot coordinates & orientations w/ gnuplot
Add acceleration attr to manu entities, load from constraints
Handle domain / out of bound errors in Motel#angle_between
omega-movement-plot: add cli param to specify static graph labels
Stop when facing intended dir in TracksLocation#rotate_* methods
Add acceleration parameters to linear movement mix

Acceleration is broken into direction components and
magnitude.

Also supports optional max_speed after which point velocity
will no longer continue increasing.

Added TODOs around parameteric / variadic acceleration and
rotational acceleration. Specs for new functionality coming soon
Update linear/follow/figure8 strategies to use acceleration

linear: accepts a dacceleration parameter similar to dorientation
        which if set will update movement strategy acceleration
        direction to match location's orientation on every
        movement cycle

follow: set acceleration and not velocity after updating
        locations' orientations

figure8: again use acceleration instead of velocity when updating
         strategy, also introduce parameter to scale linear
         acceleration when location is rotating

Specs still need tbd, coming soon
Update manu::follow to specify strategy acceleration args