Handle umbrello as KF5, without macro injection

The documentation is not tracked in the KF5 folders because it still
used the old DTD, so it is not going to be copied.
The macros have been added already to the main CMakeLists.txt of
umbrello. Injecting them here would have required a specific code
branch due to the current hybrid code of umbrello (i.e. a special
if for the KF5 case).