KDE 5 versioning in documentation

[T.C. Hollingsworth]

While reviewing some major changes I made to the Kate documentation
for Kate 5, Luigi Toscano noticed I changed "<releaseinfo>3.12 &kde;
4.12</releaseinfo>" to  "<releaseinfo>5.0 &kde; 5.0</releaseinfo>"
without thinking.

I guess "KDE 5.0" isn't going to be a thing in the future, so that
begs the question as to what to change this to in all our
applications' documentation.

For things in the workspace, I guess we'll just want
"<releaseinfo>&kde-plasma-workspaces; 2.0</releaseinfo>" or so?  Easy
enough.

Will the "KDE Software Compilation" still be a thing in the KF5 era,
complete with its own versioned releases?  If that's the case, we'll
probably just want to change "KDE" to "KDE SC" in the <releaseinfo>
for frameworks-based apps and call it a day.

If we're instead going to release all applications on their own
schedules, we'll instead probably just want to drop any mention of a
KDE version in applications' documentation.  (Or add "on KDE
Frameworks 5" or something like that?)

I'm also going to submit a review request shortly adding entities for
all this new nomenclature so we can refer to it consistently in
documentation in KF5-based applications.  People interested in this
sort of thing please double-check it for accuracy..

Thanks!
-T.C.