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)