* Abstract out non-UI code to separate DLL
This change seems rather large, but it's mostly just moving anything that is not directly driving the UI to its own, separate library. This will make it easier at a later date for any UI improvements or changes as well as making the code much more discrete. One TODO has been added as a result of this change.
* Remove MessageBox from library
This change removes the last UI-driven elements from the library. This now makes the library (in theory) UI-agnostic and removes the TODO.
* Options is more UI-related
* Fix Nuget references in csproj
* Add Winforms UI
This is a clone of the current WPF UI but implemented in Windows Forms. WPF is not currently supported by Mono for Linux and macOS, so this can provide an alternative to those users who want to run on those systems instead. This also adds a second artifact for the Winforms build.
