This makes it possible to install and then use it. Installation is still
commented since we can't give enough stability guarantees for now.
In detail:
- do not actually install headers
- generate the export header into Wayland/Server
- include it from there
REVIEW:120579
Framework style build system which generates two libraries:
* KF5WaylandClient
* KF5WaylandServer
autotests are adjusted to compile again. They need to be changed to
use the libraries once the export header gets generated.