Is your feature request related to a problem? Please describe.
Emacs.app is not picked up as an external editor

Describe the solution you'd like
Set arbitrary app as editor and pass it files as arguments

Describe alternatives you've considered
Painstakingly list every editor in existence or gently remind people to switch to Atom

Teachability, Documentation, Adoption, Migration Strategy
Use the current heuristic to list known editors, have a button to select the application/path to application outright below it.