Added last ingestion times to debug/status output.

Debug status now has an "ingestion" entry with details of the last ingestion.
I wonder if, when there's an ingestion in progress, we should just say:
"started %s, not yet complete".

Alternatively, I think we would like to know how long the ingestions are
taking even if there's one in progress, so how about these messages?

    started 2015-01-01T01:01:01; previous duration 5m4.456s
    finished 2015-01-01T01:01:0; duration 5m4.456s

(that would require a little more info gathering, but perhaps worth it)