Rebrand disman-doctor tool as dismanctl

[romangg]

The tool is supposed to become a generic information and control utility for the D-Bus backend service. In particular for starting the service on startup the tool needs to active the service if no other consumer is around (for example a non-Plasma session without KDisplay KDED daemon module). Here the "doctor" sounds wrong.

Other possible improvements:

• Add watcher mode with dicmanctl -w what keeps the tool running and prints to stdout all config changes.
• On dismanctl invocation without any arguments print out some general information without (!) activating the backend service. In particular say if D-Bus is available at all.

[romangg]

mentioned in commit 434d71d523b294b39570355b70ebb7d620703774