R1:a1a89589b1c0

Make the Dashboard dropshadow a little lighter and turn panel management into a menu

Summary:
Depends on D20372. Ref T13272.

- There's a very heavy dropshadow on panels right now that looks out of place. Reduce it a bit.
- Panels currently have unlabeled pencil and trash icons. Turn this into a menu. I'm likely planning to add options like "Change Query..." to this menu to make managing some types of panels easier.

Test Plan: {F6332838}

Reviewers: amckinley

Reviewed By: amckinley

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