Primisify createSchema() ready for migration patches
Automatically update the database when a new patch level is required

We don't automatically downgrade the database for previous patch
levels since that could be dangerous. Instead, any reverse patches
should be applied manually.
Add a bin/db_patcher.js script, run it with start-local.sh
Make sure bin/key_server.js checks what the db patch level is
Minor tweaks from review of Issue #494
Merge pull request #643 from chilts/issue-494-db-migration-strategy

Issue 494 db migration strategy