Summary:
On older versions, install(TARGETS target PUBLIC_HEADER) does not seem
to work too well, so just use install(FILES) for now. In addition, the
Qml and Quick components were missing from the main CMake file.

Test Plan: Still builds and installs

Reviewers: #plasma, romangg

Reviewed By: #plasma, romangg

Subscribers: romangg, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D28217