Variant ingredients could not be selected

[DaleStan]

Fixes #260, and adds some tests that will help prevent it from happening again. No changelog entry because this was introduced after 0.8.1.

Besides the unit tests, I also confirmed the UI correctly handled fluid variant selection for both fuel and ingredients, and that the links behaved correctly in the supplied project page.

[Dorus]

I can confirm this solves the issue in #260.

Probably your test coves this, but i find it hard to fully understand them easily so here are the scenario's that would need testing:

Swapping out a fluid ingredient for a hotter one, the new recipe should now be in that row.
Link the hotter recipe (with rightclick), the hotter recipe should now have a link. The current row should have that link.

Production and consumption of each temperature of the ingredient should individually add up on extra products or ingredients throughout these tests.

[shpaass]

Swapping out a fluid ingredient for a hotter one, the new recipe should now be in that row.
Link the hotter recipe (with rightclick), the hotter recipe should now have a link. The current row should have that link.
Production and consumption of each temperature of the ingredient should individually add up on extra products or ingredients throughout these tests.

@Dorus, do these scenarios pass when you playtest them?

[Dorus]

Yes, those are the scenarios I've confirmed to be working now.

[shpaass]

Since the playtesting passes, I'm merging it now to not keep the feature hostage.
@DaleStan, you are free to add tests as another PR whenever you want.
@Dorus, you can create an issue about the tests if you want.