[Feature Request] Add an IWAD Selection Menu to Helion

[MasterO2]

Given that Helion supports Ultimate Doom, Doom II, TNT, Plutonia, and Chex Quest, users should be able to select via a GUI which game they want to play without having to set this manually at the command line every time they run Helion.

[nstlaurent]

This is done for the next release.