Unit-tests, command line tools, and GUI tools listed by modules.

* File Naming Conventions:

- Unit-Tests pattern:                   *_utest.cpp/.h
- Command line tools pattern:           *_cli.cpp/.h
- Graphic user interface tools pattern: *_gui.cpp/.h

The front of file name must describe the goal of the tests/tools.

* All test implementations must uses DIGIKAM_TESTS_LOG QtDebug space defined in digikam_debug.h.
  To show debug traces on the console, turn on the env. variable QT_LOGGING_RULES with "digikam*=true".

* No need to support translations in this area.

* With command line tools, try to use QCoreApplication instead QApplication when possible.

* All data test files must be hosted on this git LFS based repository:
https://invent.kde.org/graphics/digikam-test-data

See class from dtestdatadir.h to manage data test files at run-time, from developer computer and on CI VM.
