♻️ Scanner and background task rewrite

[aaronleopold]

Resolves #102

Too many changes to highlight, but the overview:

• Refactor chunks of the scanner logic
• Refactor the entire job system
  • Jobs now have outputs, e.g. the count for created media/series etc
• Add support for persisted logs during job execution
  • Dedicated section in settings for logs now
• Add support for streaming logs directly from the log file on the server

I've added a new experimental workflow, so these will land there at first until I do enough testing.

@JMicheli Thanks for your help in getting this going!