Add systemd buildrequires and requires
Bump the rev in the spec
First try at a systemd service definition file, install it from CMake.

Native systemd support is enabled with cmake -DUSE_SYSTEMD=ON

Refs #4794
Fix CMake escaping.

Refs #4794
Systemd can't resolve variables recursively.

Refs #4794
Reloading with systemd is fixed now.

Refs #4794