Handle verbose logging with Log::Message::Simple

We do logging through a global subroutine in the calling program. This
won't scale very well as more programs are added. Move logging to the
Client class, and make it use the Log::Message::Simple class for this.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>
Handle errors with Log::Message::Simple

Since we use Log::Message::Simple for informational messages we should
also use it for logging errors. We already catch all errors in one
place, so all we need to do is replace our existing setup where we had
a couple of global subroutines with a call to Log::Message::Simple.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>