Use temp file for statement db to avoid connection timeout issues

[yusefnapora]

It seems that knex's connection pool doesn't like in-memory sqlite databases. It's configured to release a connection after an idle timeout, but reopening a connection to :memory: creates a new, empty database. The result is that our unit tests all pass, since they complete before the 30 second timeout, but actually trying to use the db at the repl results in your data getting erased (unless you're an especially fast typist 😄)

This just creates a temporary file with the node-temp module and uses it instead of :memory:. I set up node-temp to track and remove temp files at process exit, so we shouldn't be cluttering up the temp directory.

[parkan]

Derp. Ok