Unify the titles of examples and tutorials

The examples and tutorials in the QDS docs present a variety of naming conventions: some are titled with "example" or "tutorial", most are neither, and we even have a couple of "demos".

https://doc-snapshots.qt.io/qtdesignstudio/studioexamples.html
https://doc-snapshots.qt.io/qtdesignstudio/gstutorials.html

Let's try to decide on conventions on how to name these, i.e. what their titles should be.
Let's also examine if we can sync these names with the ones visible in the QDS Tutorials and Examples tabs to avoid confusing our users.