Introduce new extensible virtual categories for KDE
A lot of KDE Ports share MASTERSITES, LICENSE and so one, as they are
released as a bundle upstream, however, there was not really a clean
way to share this information.
Using these new categories, we can simplify the Makefiles for the diverse
KDE ports.
At the moment we support the virtual category
- kde-kde4
In the future, this will be extended to
- kde-frameworks
- kde-plasma
- kde-applications
PR: 213406
Differential Revision: https://reviews.freebsd.org/D7645
Exp-run by : antoine
Reviewed by: mat, rakuco
Approved by: portmgr (mat), rakuco (mentor)