Add db component

[oubiwann]

This should be an in-memory db. Will be used for such things as:

• storing and updating subscriber functions for the event system (subscriber registry)
• storing plugin data (plugin registry)
• refactoring blog processing into ingest ("posts" table) and stats ("stats" table)

Tasks:

• Create initial/placeholder db component, ensuring the system still works with it
• Investigate the in-memory db Clojure ecosystem
  • Datascript - https://github.com/tonsky/datascript
  • Datomic - has an in-memory mode and free starter license ...
• Select an in-memory db
• Add any missing / necessary db configuration
• Update the component to properly initialize the database "connection"
• Have the component start up datomic itself (instead of requiring it to be started on the system already)
• Also have the component kill the database process on shutdown

[oubiwann]

Done.