Add explicit requirements for jupyter notebooks examples

[363734]

Add for all example notebooks the explicit list of Python packages the user should have (in addition to cpmpy) to make the notebooks run

[IgnaceBleukx]

We can also add these requirements in the requirements.txt file like this:

numpy
ortools >= 9.6
z3-solver[full, solvers]
python-sat[full, solvers]
... # whatever other solvers
jupyter[full, examples]
requests[full, examples]
pandas[full, examples]
... # whatever is needed for the examples to run

Then a user can simply do pip install cpmpy[examples] or pip install cpmpy[full] to get the required packages.
It might be somewhat far-fetched but I think it would be a nice to have as you have gone trough the trouble of checking which packages are needed anyway :)

[363734]

If it is possible using the requirements file, it would be the best! It would simplify the life of the users and avoid the need to search all the commands to install all the packages separately

[Wout4]

The conclusion here was to not use the requirement file, since that would lead to many otherwise unneeded packages being installed (and we don't have time to figure out the optional requirements). So this should be good to merge now?

[IgnaceBleukx]

Btw what we can also do is to install the packages from within the notebook.
This way you do not need to put it in the requirements file, but also allows you to skip manual installation.

Actuallyt, any system-command can be executed using '!' before the command.
E.g., in the first cell of the notebook we can do ! pip install plotly geopy for example. Is this something we want?

[363734]

I would not recommend putting the pip install within the notebook. As the user could want to define its own conda environment to test the notebook.

It can be merge

[IgnaceBleukx]

Added everything to the notebooks, and also cleaned up the assets used by all examples. This should be a little cleaner now.
Think its ready to merge.