[dagit] Consolidate pieces into "Instance details"

Summary:
Proposed changes to the "Instance details" page and left navigation, following Scheduled Runs chat earlier.

• Remove "Daemons" page in favor of tabs on "Instance details" page, as a location to render instance-level information about schedules and sensors.
• Move "Instance details" link down to be a top-level link rather than a mini-link next to the version number.
• Move and resize left nav items following the above change.

Test Plan: Verify changes described above.

Reviewers: dgibson, prha, johann, schrockn, bengotow

Reviewed By: bengotow

Differential Revision: https://dagster.phacility.com/D5822