Add switch for KF5 (QT6) and Mod Cmake

if we want to test QET on QT6, KF5 must be removed from the code,
this switch is for that,

this is for testing only

cmake/developer_options.cmake

@@ -30,3 +30,6 @@ add_definitions(-DQT_MESSAGELOGCONTEXT)
 # You can make your code warn on compile time for the TODO's
 # In order to do so, uncomment the following line.
 #add_definitions(-DTODO_LIST)
+
+# Build with KF5
+option(BUILD_WITH_KF5 "Build with KF5" ON)