Controls for coverage graph history

[Liam-DeVoe]

We currently have controls for Together, Separate, and Latest, for the workers on the coverage graph (#175).

We should also add:

• sub-options for Separate: normal / with x-offset
• "since" date selector, filtering to workers that started since that date
  • persist between pages
  • use standard 1d/7d/30d/3mo/6mo/1yr pills, plus a full calendar selector?
  • plus a slider inside that range, like the workers page?