Resolve "refactor(doc): snake_case tutorials"

Description

All targets that were still in camel case were renamed in snake case: tutorials, examples and unit tests.

Also the naming of unit test and GUI tests were made consistent:

• the new naming for unit test targets is <target>_ut instead <target>Test.. The namespace is unchanged, target::ut.
• the new naming for "GUI" test targets is <target>_uit instead <target>GuiTest. The namespace is now target::uit instead of target::test::ui.

This frees up the "_test" suffix for library test code, i.e. the test of module_ui does not conflict with the test library module_ui_test.

We must merge first sight-data!18 (merged)

Closes #1188 (closed)

How to test it?

Unit-tests should be sufficient, but you can test some apps.