OSX - 3.20.0 (r6) - Mojave

3.20.0 pre-release version

This is a pre-release version. I'm attempting to mainly test the build environment. While having some issues, I still think it's useful to draft a release with this version.

For Osama

This version is dedicated to my brother, Osama, who was killed in the Christchurch terrorist attack. If you use/like this software, please pray for him.
https://www.stuff.co.nz/national/christchurch-shooting/111375038/osama-abu-kwaik-was-a-refugee-born-to-an-orphan-who-died-in-christchurch-the-city-he-loved

What's new

1. Upstream 3.20.0. We need to build gtksourceview version 4 to move to newer versions.
2. Added some fixes that will hopefully fix the saved-state issue that appears on OSX.
3. Added some OSX features to simplify working from within terminal

What's broken

1. Minimize button doesn't work
2. Gtk feels too slow for my taste. I will experiment with Gtk4 + Vulkan backend instead of Quartz backend in the next phase
3. Min/Restore/Max buttons are not native. This will likely require some interesting work-around.