Added basic CMake setup, including unit tests

[benthevining]

• Added basic CMake setup to allow installation of foleys_gui_magic as a CMake package
• Added a unit test runner in the Tests directory. It has only empty example test cases for now, those can be filled in.
• On the CMake side, I got rid of CPM.cmake, I've recently been preferring to use pure find_package and supply simple find modules that call FetchContent where necessary.
• The JUCE module sources have been moved into a foleys_gui_magic subdirectory. This makes it easier to call the JUCE cmake functions for setting up the module, they expect a very specific folder structure

Possible future work:

• Creating test cases for the unit test runner to execute
• Additional integration tests other than the UT runner -- perhaps building a test project that depends on the foleys_gui_magic module?
• Setting up tests to run on CI

[benthevining]

I've just updated:

• Moved module sources back into repo root, no more nested foleys_gui_magic/ directory

[benthevining]

I've just updated the unit tests GitHub workflow file.