Add logger message count to MOTD

[mnishiguchi]

resolves #80

Notes

• This should be on hold until Make the MOTD more concise #96 is resolved since this adds more info to the MOTD
• Related PR: Add count_next function ring_logger#99

TODO

• update RingLogger to return statistics on types of messages
• adjust the count

[fhunleth]

I had a thought on this feature based on some recent usage: I'd like to know if I have any messages that are warnings or errors as well. For example, I'd probably ignore 196 info/debug messages most of the time, but if I saw that there was an error, I'd definitely check the log.

This would require an update to RingLogger to provide counts based on types. Since the function that was added to return the unread message count hasn't been officially released, I think that we can update it to return statistics on types of messages.