Provide macOS application bundle

[JaapJoris]

The Windows installer of IA Launcher was created with cx_Freeze which also has the capability to generate a macOS Application bundles. It should be as easy as running the following command:

$ python3 setup.py bdist_mac

In practice, however, there's bound to be lots of little macOS peculiarities that have to be taken care of. Since I don't own an Apple computer, I am unable to dive into this further. If anyone is interested, feel free to help out!