CMake files still too repetitive

[sraaphorst]

The CMakeLists.txt files for the projects within src are too repetitive. They should instead just need to define public headers, private headers, and source files, and then call a function to do the rest.

Similarly, in the src/CMakeLists.txt file, we should only have to have a list of subpackages, and use functions to do all the rest of the work to avoid the repetition.

[sraaphorst]

Cleaned up significantly. Now Qt code is only in gui directory, and each package only contains a list of its PUBLIC_HEADER_FILES, PRIVATE_HEADER_FILES, and SOURCE_FILES.