Update tutorials & create new ones

[clizbe]

Go through each of the tutorials and see if they still work and are followable.

• Simple system tutorial (735 tutorials tarskul #754)

Otherwise, adapt the other tutorials to examples or how-to sections:

• two hydro power plants
• case A5

Also, create new tutorials:

• Create a tutorial for flexible temporal resolution #780
• stochastic structure
• capacity planning
• Create a Multi-Year Investment tutorial without using economic representation parameters #914
• Create a Multi-Year Investment tutorial focusing on how to use economic representation parameters #1070
• Create a tutorial to use the unit commitment constraints #765
• Create a tutorial to define reserves constraints #751
• Create a tutorial to create a rolling horizon model #974
• PTDF (may be a how-to?)
• custom constraint
• Benders
• MGA
• Inertia (see Express reserves and inertia explicitly in the input data #774)

As well as how to's:

• pressure driven gas system
• storage

And update the documentation accordingly:

• text in the overview of the documentation
• json files for the tutorials

[clizbe]

Related: #436, #459

[tarskul]

I've updated the simple system tutorial with the experience from my own struggle, mostly explaining some things in more detail (e.g. the three-way relationship for defining an efficiency) and adding some warnings for pitfalls (e.g. messing up the order in the three-way relationship). Besides the pitfalls, the tutorial seems fine.

[tarskul]

After some deliberation, only the first tutorial is a real tutorial. The other two should be adapted to examples or how to sections.

Then we should also add some new tutorials that cover more features of SpineOpt.

I'll edit the issue description and we should later have a discussion on these new tutorials.