few more tweaks to segment revisions to account for case where we are comparing against nil object for initial revision.

if initialization throws an exception then exit the app.

extend `rows` column from integer to bigint so that we can support large row counts.

Conflicts:
	frontend/src/lib/query.js

* updated IRevisioned protocol to add a `(diff-map)` function which provides a structured description of the change.
* renamed `(describe-diff)` on IRevisioned protocol to `(diff-str)` just for naming consistency.
* reworked some of the code around how revision details are added to revisions
* new default version of `(diff-map)` for existing revisions objects
* cleanup on unit tests, etc.

Bump dependencies 

Fast implementation of `active-tables` for SQL DBs