Code now relatively gracefully handles trying to solve a solved cube

[jbwincek]

I made progress in other areas before noticing this issue #10. But I wrote a quick fix for #10 which is included in this pull request.

Added In this pull request besides that is:

• this commit which makes it possible for pycuber.solver.CFOPSolver.solve() to not display any of the progress updates.
• Some tests verifying pycuber.reverse()
• and pep8-ification so my linter would stop underlining so many things, hence so many diff highlights, sorry.

[adrianliaw]

Hey @jbwincek, thank you for reminding me about this and opening this pull request, but there are some modifications where I think will be more appropriate to use another solution:

1. Suppressing progress output is done perfectly, but I think we should use optional suppress_progress_messages argument like you did in b6acc05e01dd1760034f5e0de4c7b68c9d2e4420.
2. When solving a solved cube, I think it's more appropriate to use enumerate to enumerate through every F2L slot instead of raising an error. I actually noticed this problem before, I thought I've solved this... Maybe I forgot to push.

Anyway, I'll merge this and I'll fix them on my own. Thanks a lot!