Add kate to kdesrc-build's kf5 file.

Try to split up the file internally into 3 sections:
frameworks, workspace and apps, matching the future releases.

This raises some interesting questions:
* should attica become a framework?
* should phonon become a framework?
* should kactivities become a framework?
* are we sure nothing in frameworks+workspace will depend on kate interfaces?

CCMAIL: kde-core-devel@kde.org