Added lost of tests for SimplicialComplex class

[maximelucas]

• added lots of tests
• changed the behaviour of inherited Hypergraph methods such as add_edge: instead of raising an error and not adding the simplex, we now add the simplex and raise a warning.
• a consequence of the previous point is that some HG methods that did not work for SCs now do (and raise a warning): e.g. copy()
• added tests to check the new warnings and other old warnings
• fixed an off-by-one in update_uid_counter bug in add_simplices_from when specifying uid #243

The cleanup of the SimplicialComplex is not finished yet but I feel like this PR is getting big already.
There is one test that does not pass, due to #244. I feel like fixing it would be a lot of code change and would be better in another PR. (The test is new and the fact that it does not pass just highlights a pre-existing bug)

[leotrs]

Thanks for all your work here. So your suggestion is that we merge this now as is and then fix the broken test in a different PR?

[maximelucas]

Yes exactly. Because fixing it will require to rewrite the add_simplices_from function as non-recursive and change the order in which simplices are added, so we will probably need to update existing tests too. Is that allowed by Github?

[leotrs]

Great! I'd suggest we merge this and then get on working the next PR asap.