Fixes #257

Terminal.app does not inherit environment variables.
Therefore, expand environmet variables in the script.

We were missing the filesystem watcher library port
for macOS, this adds it.

Fixes #227

Fixes #228

reference from https://github.com/msysgit/msysgit/wiki/Git-for-Windows-Unicode-Support

* Changes direct usages of GUI.enabled to instead use EditorGUI.BeginDisabledGroup() / EditorGUI.EndDisabledGroup()