Pyp5js

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- Fix bug of null `_P5_INSTANCE`

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- Display sketch with code
- Add ACE editor to edit the sketch code
- Add aliases to Processing.py functions & constants (`size`, `pushMatrix`, `popMatrix`, `pushStyle`, `pushStyle`, `P3D`)

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- Fix issue with assets

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- Update sketch's template
- Add unit tests to the Flask API
- Base style for the web client

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- Validate sketch name
- Add base templates for the web app
- Add iframe with example 000 to the index

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- Ensure the sketchbook dir always exists