Esparto

- Fix linting errors.
- Add dataclasses dependency for Python < 3.7.

- Fix bug corrupting document titles.
- Lazy load the content dependency dict.
- Remove unused code.

- Make documents 'print friendly'.
- Output to PDF with weasyprint.
- Export matplotlib plots as SVG by default.
- Use `esparto.options` for configuring behaviour.

- Fix notebook display for Colab.

- Add Bootstrap dependencies for relevant content classes.
- Inherit FigureBokeh height from Bokeh object.
- Fix issues with in-notebook content rendering.

Added support for:
* Bokeh
* Plotly