0.4.0: More visualization options, 3D manipulators, and icons

0.4.0 focuses on improving the 3D visualizer in the model editor tab by adding things like custom visualization options, 3D manipulation gizmos, and graphical improvements. Overall, 0.4.0 contains ~50 changes over ~200 commits. See the CHANGELOG for more details.

Highlights:

• Added 'Lines of Action (effective)' and 'Lines of Action (anatomical)' rendering options to the model viewer
  (#562). They can be seperately toggled for muscle insertion/origin (#577). Clicking a line of action selects
  the associated muscle (#571). Thanks to @modenaxe for open-sourcing https://github.com/modenaxe/MuscleForceDirection
• Stations (#85), PathPoints (#85), PhysicalOffsetFrames (#583), WrapObjects (#588), and
  ContactGeometry (#596) can now be translated (or rotated, #584) in a model editor viewport with a
  clickable gizmo
• The editor and simulator screens now have toolbars at the top containing common actions (e.g. undo/redo,
  save, load, scrub the simulation, etc.)
• OSC's logo was updated to make it visually distinct from OpenSim, and new icons have been added for toggling
  frames, markers, contact geometry, and wrap surfaces
• Shadow rendering is now default-enabled (#489). The scene light's slope/height no longer tracks along with the camera, which makes the shadow angle look a little bit better (thanks @tgeijten, #549)
• The "Reload [Model]" button now forces OSC to also reload any associated mesh files, which is handy when seperately editing mesh files in something like Maya/Blender (thanks @JuliaVanBeesel, #594)
• Hotfixed a bug from OpenSim where inertia edits were not applied to the model (#597, related: opensim-core/#3395, thanks to @jesse-gilmer for spotting this :))
• ... and many other changes (see the CHANGELOG)