Install mimetype definitions for kcfg/kcfgc/ui.rc/knotify & qrc files

Summary:
When browsing folders of sources with KDE software, e.g. in Dolphin or
KDevelop, there are currently quite some files shown to be only simple text
files, despite being well-known special ones.

This patch adds mimetypes for a few typical special formats as used in
software building on KDE Frameworks and Qt.

Reviewers: Frameworks, dfaure

Reviewed By: dfaure

Subscribers: ngraham

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D8728