Database tracker is able to detect changed values

For more info & context, read the Use Case in #44.
## Story

When user tells the database tracker to create a commit (see #41)
Then it detects the changes
and converts them to blocks in a jawn commit
And writes the commit to the feed in jawn
## Additional Info
### What kind of Database?

For now we will assume sqlite.
### How does it figure out what changes have occurred?

The database tracker will need to be able to compare what's in the jawn feed and what's in the database.

Either way, the feed should have info about when data was last pulled from the database.

Option 1: Parse the database log
Option 2: If the database tables keep a "last updated" timestamp then we can just query for things that have been updated since the last time the feed was updated. -- we can either ask the Open Data team whether their data has this info, or we can read up on ArcGiS ourselves.