[Shared] New and seperate icons for all executables

[SomaZ]

This replaces all icons with a new set to show the difference between OpenJK SP, MP, OpenJO and the dedicated server.

OpenJO can and has a seperate Icon than OpenJK SP now.

All windows icons are now in the shared folder, while the macos icons are still in their respective subfolders. Wasn't sure if one could use relative paths for icons for mac builds.

openjkcmd.ico was contributed by @SirYodaJedi

MacOS testers are welcome as I don't own Mac hardware :)

Edit: Add screenshot for simple preview of how these look on windows:

Fixes https://github.com/JACoders/OpenJK/issues/630