cmake: shorter directory names, clearer hierarchy

CMakeLists.txt

cmake/bornagain/CMakeLists.txt

cmake/bornagain/modules/BornAgainCPack.cmake

cmake/bornagain/modules/BornAgainConfiguration.cmake

cmake/bornagain/modules/BornAgainMacros.cmake

cmake/bornagain/modules/CPackApple.cmake

cmake/bornagain/modules/CPackDebian.cmake

cmake/bornagain/modules/CPackWindows.cmake

cmake/bornagain/modules/CheckCompiler.cmake

cmake/bornagain/modules/FixAppleBundle.cmake.in

cmake/bornagain/modules/GeneratePythonDocs.cmake

cmake/bornagain/modules/NSIS.InstallOptions.ini.in

cmake/bornagain/modules/NSIS.template.in

cmake/bornagain/modules/SearchInstalledSoftware.cmake

cmake/bornagain/modules/SetUpLinux.cmake

cmake/bornagain/modules/SetUpMacOS.cmake

cmake/bornagain/modules/SetUpWindows.cmake

cmake/bornagain/modules/UnitTests.cmake

cmake/bornagain/scripts/BAConfigure.h.in

cmake/bornagain/scripts/BAPython.h.in