Mac Support

It would be nice if we could have the Maya plugin work for both Windows and MacOS, however there's alot of work needed to get it to a state where we can even build for MacOS.

- [ ] refactor out Windows-specific .NET Standard libraries to use portable, .NET core compatible solutions
For example, we are using `System.Windows.Forms` for our GUI and `System.Drawing` for a number of structures and functionality. Also, we are using `SharpDX` for our matrix math in `Tools` for instance. We may want to get an exhaustive list of windows-only dependencies we're taking
- [ ] Redo GUI
Since we'd need to move away from Windows Forms as our GUI solution, it follows that our GUI would need to be recreated in whatever solution we choose. This is definitely not a trivial task, given the ~dozen of views we have for this project. It may be a good time to consider redesigning how we want to present the different functionality we provide across the different controls. I would expect that we would want to reuse as many controls as possible between 3dsMax and Maya.
- [ ] standup mac OSX build
I'm not sure how the plugin format differs between Maya for windows and MacOS, but if we cannot reuse the Windows build binaries on MacOSX, we would have to standup some CI system for MacOS as well.

The issue names no files, tests, or entry points; begin by inventorying the Windows-only .NET dependencies, GUI views, and current Maya build process. Done would require an agreed portable GUI approach, Mac-compatible dependencies, and a reproducible Mac build, but the scope and acceptance criteria are not defined.

Written by the indexing model from the issue text.