Require CMake 3.16
Fixes
CMake Warning (dev) at /usr/share/ECM/modules/ECMFindModuleHelpers.cmake:113 (message):
Your project should require at least CMake 3.16.0 to use FindKF5.cmake
Call Stack (most recent call first):
/usr/share/ECM/find-modules/FindKF5.cmake:30 (ecm_find_package_version_check)
CMakeLists.txt:49 (find_package)
This warning is for project developers. Use -Wno-dev to suppress it.