feat: rewrite Teaching Stats

[ChiaraZuccaro]

Related to UNICT-Quality-Development/qd-projects#46

In this PR:

• (MAIN) Teaching stats on selection (style will be improved);
• Info disclaimers for OPIS groups (V1, V2, V3);
• Unit tests for all utils;
• Unit tests for graph.service and cds.service;
• Buttons to switch graph type (disabled while loading);
• Added descriptions for each graph type.

[Helias]

not sure if it makes sense to exclude the *.html files

[Helias]

I think that what you are doing is more than the average request effort for this kind of project, you are rewriting the entire application, good job 🚀 💯 .

Tips:

• make smaller PRs, so the review will be better, more detailed, and faster
• would be great before making a new branch and PR to align the commit history, so update the fork with the upstream development branch (UNICT-DMI:development) and build on top of it, so the commit history will be compact and clear

[Helias]

I have found a bug testing it in https://unict-dmi.github.io/OPIS-Manager/development/department/matematica_e_informatica

I am afraid that the URL does not work properly, we should enable hashroute to fix it