New type of probe: PID

[MadJlzz]

Is your feature request related to a problem? Please describe.
This feature is about providing probes a way to check a living PID on a local/remote hostname.

Describe the solution you'd like
Whenever a probed service PID is not existing anymore, the status of the probe should be set to DOWN.
To connect to a remote host, consider using SSH with either username:password and public and private keys.
Also, refactor the existing to allow a more flexible way to implement new probe types.