Add number of rows of data saved to our system graphs so we can better understand when data stops being recorded

[equivalentideas]

According to #1064 we're a bit stumped as to why scrapers stop writing to the database sometimes. We're seeing this bug a lot, and it's very bad for users.

If we were tracking the number of rows being written by scrapers over time on our graphs page, we might be able to better connect this event to whats happening elsewhere in the system.

http://graphs.morph.io/dashboard/db/morph