Make modpack mostly independent from MTG

[TurkeyMcMac]

This PR makes all Mesecons mods except mesecons_doors work with any game, and none of the mods hard-depend on default any longer. I added a mod mesecons_gamecompat to handle most external dependencies. The addition of a mod to the pack may cause problems for people updating it, in which case I should put the compatibility code in the mesecons mod or something. In any case, almost the entire modpack will now work with any game, although it requires default and some other MTG mods to provide sounds etc.

mesecons_detectors depended on default to provide default_steel_block.png. To remedy this, I added a copy of the texture to the mod as a fallback (giving appropriate attribution.) I could make the mod use the fallback texture 100% of the time, but this might mess with existing texture packs.

If no mesecons_gamecompat:mese alias is registered, mesecons_extrawires provides its own placeholder mesecons_extrawires:mese. Otherwise, mesecons_extrawires:mese is an alias of the real mese.

Support for more games without the default mod can be added in the future by adding more compatibility code to mesecons_gamecompat.

[sfan5]

Nice.
To me mesecons_compat sounds more like internal backwards compatibility maybe mesecons_gamecompat would be a better name or you have a different idea.
I'll add some more comments in a review below.
Also what about the list inside mesecons_mvps?

[TurkeyMcMac]

I'm not sure about changing the list in mesecons_mvps, since mods might want to register the MVPS stoppers for themselves.

[sfan5]

I'm not sure about changing the list in mesecons_mvps, since mods might want to register the MVPS stoppers for themselves.

I don't understand the concern here. There is a hardcoded list of nodes in the mod, surely it should only apply when MTG is detected?

[TurkeyMcMac]

Yes, my thought is that the list should apply only when MTG is used, and other games that Mesecons is made compatible with can register their stoppers themselves.

[sfan5]

Then what about moving the hardcoded list to mesecons_gamecompat, inside the MTG part?

[sfan5]

Works, tested with devtest.

[TurkeyMcMac]

@Tim79000 default contains a lot of unrelated features, many of them specific to Minetest Game and its spin-offs. If a mod depends on default, it basically depends on Minetest Game.