attica : move Qt4/KDE4 headers and add Qt5 subport

[RJVB (René Bertin)]

This supersedes and replaces ticket #49109 , and depends on ticket #49595

• attica (for Qt4/KDE4) installs its headers into ${prefix}/include/attica, where they can be picked up instead of those from the KF5 version (port submission pending). Rather than fixing the the build system in an unknown number of dependent ports, it is more convenient to move the headers of the KDE4 version into the KDE4-specific headerfile prefix which is required anyway (see ticket #49595).

(Note that revbumps shouldn't be required for this kind of change.)

• adds a Qt5 subport. I'm not convinced this one is very useful once kf5-attica is available; it should probably be marked as replaced_by that one, in due time. See #49109 for the Qt5-specific patchfiles.