bsd.kde4.mk: Add KDE4_APPLICATIONS_{VERSION,BRANCH}.

At the moment they correspond to the latest KDE Applications release with
mostly KDE4-compatible applications.

These are going to be used by the upcoming DigiKam update (some ports have
been split off the main DigiKam tarball and are part of the regular KDE SC
releases). It will also be used once we add KDE Frameworks 5 and Plasma 5 to
the tree.

PR: 204623