Move away from stylistically ugly camel case for CMake targets. We use the
commonly used kebab-case instead for installed targets and ensure that these
names are unique even if being called from within other projects.

This allows packagers to build specific targets easily, of which there are:

Libraries:
* disman-lib
* disman-wllib

Executables:
* dismanctl
* disman-launcher

Backend plugins:
* disman-randr
* disman-wlplugin

Wayland backend plugin plugins:
* disman-kwayland
* disman-kwinft
* disman-wlroots

BREAKING CHANGE: target and library names change