Add status endpoint

@jh-bate @kentquirk 

Needed a status endpoint on tide-whisperer.  This is a quick pass at it.  It's working locally, pls review and merge.
I have no problem with that.  OK is fine.  I'm also fine with like 

`{mongo: up}` or something like that too.  Just tell me "Make it XXX" and I will do that.  I've generally figured that it didn't matter until we had something that was actually watching these and when we did that, we'd probably figure out that we did it wrong anyway...