Speedup dashboard

[mveytsman]

First pass at speeding things up, bears dashboard goes from 12s to <6s on my computer

• Made loading last_heartbeat_at very fast
• Sped up query to find whether a bundle is vulnerable
• Disabled loading processes if you don't have the rollout
• Loaded all tags per server

I think there's still a lot more to be gained by speeding up the vulnerable query

TODO:

• [x] fix tests
• [x] add partial index:

  CREATE INDEX vulnerable_dependency_no_patched ON vulnerable_dependencies (id)
  WHERE (vulnerable_dependencies.affected_versions != '{}'
         OR NOT (vulnerable_dependencies.patched_versions = '{}'
                 AND vulnerable_dependencies.unaffected_versions = '{}')