This fixes a few issues with Atlas that prevent it from working on Catalina:
- Remove the 'osxguiapplication' override. This fixes the editor starting up in the background and not accepting input.
- To prevent an issue with sdl/wxwidgets conflict when running from inside the game, actually boot a new instance (see #2427)
- Fix an assertion error because we try to use SDL subsystems that aren't initialised.
- Fix key events not being correctly sent to the game since we upgraded to SDL2 and use SDL_TEXTINPUT for text (see #2846)
The last remaining thing is the retina-size issue, which is fixable (see wik's post) but needs work.
D2752 is not technically a prerequisite, but you can't test on catalina without it.
This is cleanup work form issues reported by user wik on the forum, see: