Startup Box showing options for template, recent projects, and changelog

[ermannolocascio]

Fixes #2589

Progresses

• 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 to the spine data structure: https://github.com/energy-modelling-workbench/spine-data-model#spine-data-model
• Setting up a workflow: mention the section "Adding a Data Connection Item to the Project"
• executing projects: https://spine-toolbox.readthedocs.io/en/latest/executing_projects.html

Template tab

Checklist before merging

• Documentation is up-to-date
• Release notes have been updated
• Unit tests have been added/updated accordingly
• Code has been formatted by black
• Unit tests pass

[codecov]

Codecov Report

Attention: Patch coverage is 61.30742% with 219 lines in your changes missing coverage. Please review.

Project coverage is 67.05%. Comparing base (aa5c7bb) to head (d118f7b).
Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
spinetoolbox/opener_tester.py	0.00%	173 Missing ⚠️
spinetoolbox/widgets/startup_box_widget.py	69.44%	32 Missing and 1 partial ⚠️
spinetoolbox/changelog_diff.py	64.28%	5 Missing and 5 partials ⚠️
spinetoolbox/ui_main.py	85.71%	1 Missing and 1 partial ⚠️
spinetoolbox/ui/startup_box.py	99.58%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2740      +/-   ##
==========================================
- Coverage   67.13%   67.05%   -0.09%     
==========================================
  Files         193      197       +4     
  Lines       37011    37574     +563     
  Branches     4443     4465      +22     
==========================================
+ Hits        24847    25194     +347     
- Misses      10912    11115     +203     
- Partials     1252     1265      +13     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.