Do not show charts at the end, close charts after being used

[hugo-dc]

Fixes #154

Also, closes all charts after being used in order to not retain in memory, avoiding the warning message RuntimeWarning: More than 20 figures have been opened. Figures created through the pyplot interface (matplotlib.pyplot.figure) are retained until explicitly closed and may consume too much memory. (To control this warning, see the rcParam figure.max_open_warning).

[lgtm-com]

This pull request introduces 104 alerts when merging d35b66f into a156a28 - view on LGTM.com

new alerts:

• 53 for Use of the return value of a procedure
• 51 for Variable defined multiple times

[lgtm-com]

This pull request introduces 4 alerts when merging d35a61e into f1ed847 - view on LGTM.com

new alerts:

• 3 for Use of the return value of a procedure
• 1 for Variable defined multiple times

[lgtm-com]

This pull request introduces 4 alerts when merging ad90868 into f1ed847 - view on LGTM.com

new alerts:

• 3 for Use of the return value of a procedure
• 1 for Variable defined multiple times

[jwasinger]

@hugo-dc The CI generates the charts in a non-GUI environment which results in smaller resolution images, and is the reason this PR fails CI currently.

[hugo-dc]

@jwasinger I created a Dockerfile to generate the charts in a docker instance, but it is generating the exact same files (no diff), I'll take a closer look at the CI and maybe try to use the same versions of the tools (OS, python, jupyter,etc).