Add warning when selecting non-free license

[Wuzzy2]

When the user selects a non-free license, I suggest to make a warning pop up.

That would be the case for the following options:

• CC BY-NC-SA 3.0
• Other (Non-free/closed)

The warning should talk about that non-free anything doesn't really align with Minetest's ideals or something like that and that they are merely tolerated, here. And about that rating punishment for non-free things.

For the special case of “Other (Non-free/closed)”, the warning should also say that the license still must allow derivs.

But maybe it would be better to just remove the “Other” option altogether. I don't think it's a good idea to

1. Allow proliferation of obscure licenses in the first place
2. Let the poster judge whether their obscure license is free or non-free (especially when those terms are unqualified)

[ghost]

But maybe it would be better to just remove the “Other” option altogether.

Maybe remove all licenses that are neither OSI approved nor FSF approved.

[rubenwardy]

Packages with an "other" license cannot be approved, the purpose is for the submitter to let me know to check the license and add or reject it