During plasma startup we have multiple processes using kactivities at
once. The current code looks to see if the bus is active then launched
the executable.
If this happens at once, we end up loading, doing all the
initialisation only for all-but-one of the services to fail to register the name
and then quit.
By using DBus activation, we get that global lock in a very safe way.
This requires a change (a .service file) on the daemon, so a fallback is
provided for 5.11 support
