0.5.16: Muscle color scaling, smaller installer, and more documentation

0.5.16 is a patch release that focuses on improving how the software is packaged and its documentation, with a few nice-to-haves thrown in for good measure. Read the CHANGELOG.md for a full list of changes, here are some featured ones:

• There is now a Color Scaling option in the muscle coloring/styling panel, which enables auto-scaling the min/max (e.g. blue-to-red) color range based on the model-wide min/max of the chosen Color Source. This is useful for visualizing differences between muscles that are all within a tight numeric range (#933).
• The installation, building, development environment setup, and contribution guides have been moved into the documentation pages (https://docs.opensimcreator.com/), so that there's a centralized location for all documentation.
• Finished off tutorials 5 and 7 in the documentation.
• After dragging a file into OSC, the next file dialog that opens should now default to the same directory that the files were dragged from (thanks @mrrezaie, #918).