Typo fixes and warning removals in Johansson lecture series

[NiallCarbery]

• Fix of typos in lecture series v4/v5
• Details added to Lecture 13, Introduction and minor graph labelling
• Zero Division warning removed Lecture 5
• Deprecation of colour in matplotlib warning resolved (v5)
• e_ops made as a positional arguement throughout lecture series (v5), warning removal

[nwlambert]

thanks for these fixes! I left a couple of small comments, let me know if it makes sense. Keeping these lectures up to date and functioning is very important, this is much appreciated!

[NiallCarbery]

Thanks for the comments! The lecture series were my preferred way to learn QuTiP as they are very general. Ground state indexing for resonance fluorescence is correct. Old habits die hard.

[NiallCarbery]

Fixes squashed into orginal commit

[nwlambert]

Sorry, two more small things; in tutorials-v5 cases, can you remove the SolverOptions import from lectures 10 and 2B? that should fix the pep8 error