Split WAD engine inquiry into basic/advanced forms

[decino]

WAD engine is too confusing for newbies and I don't think most understand the difference between e.g. Doom II and GZDoom, so split it into basic and advanced:

Basic would ask "What source port did you play or test this on?" and they can write whatever into a text field or something.

Advanced would ask for WAD engine like it does now through a dropdown list of predefined engines. For the latter I think we also need an additional "Other" option for edge cases where the map requires a very specific source port like Eternity Engine and they'll have to specify it in the description or a separate text field.

Swap between basic and advanced through a radio button.

[decino]

Better off not splitting at all. Always offer free input where the user can write the source port they've used. Optionally add a dropdown list next to it with the most used compatibility levels:

• N/A
• GZDoom (default)
• Doom II (-cl2)
• Ultimate Doom (-cl3)
• Final Doom (-cl4)
• Boom (-cl9)
• MBF (-cl11)
• MBF21 (-cl21)

Note: the default selected item should be N/A, not GZDoom's default compatibility. It just happens to be called like that.