Support optional loading of list analysis enrichment

[heralden]

Enrichment is automatically run for the results page, and is quite a heavy operation involving lots of HTTP requests. On slower computers, this causes a short freeze.

We should consider making it optional some way

• able to uncheck an Always run box in the enrichment column
• an Analyze button the user has to press to start enrichment (could also apply for all visualizations on the page)

Update: We should set a threshold of 2000 to automatically run enrichment, and once exceeded, display a message explaining why enrichment isn't run, with a button to override it.