Ermanno Lo Cascio

1. Which tutorials should we include? 2. Which templates should we include? (_Executions tests -> /execution_tests/ folder_) 3. How templates should be catogorized? Hints are very welcome.  

Fixes #2589 ## Progresses - [x] Renaming the "Tutorials" tab to "Learning materials" Include the following links with highlights - [ ] "Hello world" equivalent: https://spine-toolbox.readthedocs.io/en/latest/getting_started.html - [ ] Introduction...