Modify sidebar on extension "homepage" view

Created by: jjinnii

For users who have authenticated their account OR performed searches within the extension, the extension sidebar displays search history. However to better mirror the homepage on sourcegraph.com, we need to remove the "Search Reference" section, as well as separate out Recent History into: Recent Searches, Recent Files, and Recent Repositories.

I am maintaining Search Types (distinct from sourcegraph.com) because I've observed in user testing that many first-time Sourcegraph users used Search Types to get started.

Current state:

Expected state: Designs