Install kcoreaddons license texts

* src/inst-kcoreaddons.nsi, src/uninst-kcoreaddons.nsi: Install/
Uninstall license texts.

This automatically makes the license link in the about dialog
of Kleopatra and Okular work and covers the "You should have
received the license along with this program"

KCoreAddons is a good place because the GnuPG installer installs
its own licenses and everything else is then just dependencies for
KDE based Software.

• GnuPG-Bug-Id: T6834