Added dummy face detection node, integrated with BiteInitiation

[amalnanavati]

Describe this pull request. Link to relevant GitHub issues, if any.

In service of #27 .

Added a dummy FaceDetection node that detects a face and mouth periodically (in practice, it detects a face every ~5 secs and detects an open mouth every ~10 secs). Integrated that with BiteInitiation.jsx so that it waits for the robot to detect a face before letting the user continue, and then lets the user continue with either an open mouth or button press. It stores the detected mouth center in global state so that MoveToMouth.jsx can access it.

Explain how this pull request was tested, including but not limited to the below checkmarks.

First, I tested the face detection node by:

• Turning it on and ensuring that it didn't publish to the face detection topics.
• Toggling it on and ensuring that it does publish to both face detection topics.
• Ensuring that faces and open mouths are detected at the expected frequencies.
• Toggling it off and ensuring that it stops publishing to the face detection topics.
• Toggling it on when its already on and off when its already off and ensuring there is no change in functionality.

Then, I tested the BiteInitiation page by:

• Loading the page, ensuring it toggles face detection on, ensuring that it registers a detected face only when the right message is published, ensuring that it registers an open mouth and moves on only when the right message is published, ensuring that it toggles face detection off before moving on.
• Ensuring that when the page is refreshed it toggles face detection off (before turning it back on again when the page re-loads).
• Ensuring that the button moves it to the next state and toggles face detection off.

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• [N/A] Consider the user flow between states that this feature introduces, consider different situations that might occur for the user, and ensure that there is no way for the user to get stuck in a loop.

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[amalnanavati]

NOTE: As it stands, the UI of the BiteInitiation page involves scrolling to get to the cancel and move above plate button. I left it like this for now, though, because we will be removing the staging location (Issue #45 ), which will get rid of that page altogether.