Integrate Quirk Editor Embed in Cirq

[freyam]

This PR aims to solve Issue #4489 by integrating Quirk editor in Cirq.

Proposed Changes

• [x] [CORE] Users should be able to pull up the Quirk editor in IPython notebooks from within Cirq.
  • Added pyQuirk widget (from pyQuirk import Quirk).
  • Users can launch the editor within a notebook by Quirk().
• [ ] [CORE] Convert a cirq.Circuit to a Quirk circuit from within the notebook.
• [ ] [FEATURE] Allow modifying an existing circuit / build a new circuit using Quirk and export as cirq.Circuit from within the notebook.
• [ ] [FEATURE] cirq.contrib.circuit_to_quirk_url which can convert a Quirk URL to a cirq.Circuit.
• [ ] ... (to be discussed)

This PR is part of the Cirq Visualizations Roadmap.

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[freyam]

@googlebot I signed it!