`importorskip` statements should be used in the test suite

[Andrew-S-Rosen]

If fireworks or matplotlib (potentially others like maggma, moto, ...) are not installed, the test suite fails. It would be better to use a importorskip marker (preferable) or to update the dev optional dependencies to be the full suite of dependencies needed to run the tests. Alternatively, the contributing instructions should say to install the strict dependencies.

[utf]

I would be happy to accept a PR that skips tests if the packages aren't installed.