Add standard stream logger

Added and activated logger implementation, which will write logs to
stdout and stderr.

This way SDL logs are included to 'kubectl logs' command output
of containerized application which is using SDL library.

SDL logs starts with "shareddatalayer: " prefix.

RIC has own logging library, which will be taken into use later as
a separate commit / merge request.

Signed-off-by: Rolf Badorek <rolf.badorek@nokia.com>
Change-Id: I1b2d4085aa3112b02c4a2161e371712ea5ba2cb5