Complete rewrite of database layer

[TheTechRobo]

First commit was from February, geez...

things still to do (off the top of my head):

• Actually implement recursion. This should be fairly easy, add an API endpoint to queue pages and do that from the client. Depth should already be handled.
• Polish dashboard
  • Reimplement a few helpers
• Add !ig/!unig aliases for reject + skip rules and their corresponding removal
• Workers should report disk space to the server
• Find all the overengineered stuff :-)