Heatmap plot viz

[vincerubinetti]

Please research library options and discuss them here before starting implementation. If at all possible, I want to use a library that can handle all the general plots we may need, including: bar chart, line chart, upset plot, sunburst plot, heatmap (see the other issues in this repo).

More specific notes/guidelines:

• Should be SVG-based, not canvas-based
• Don't necessarily need exactly the same feature set as the 1.0 visualization. Layout can be slightly different, can have more/less/different customization options, etc.
• Don't implement a download button yet.

See the following comment for guidelines on implementation and general architecture:
#32 (comment)

[Sproff]

Sounds good.

We can go with Vega-Lite or D3 if we prefer a deep dive into customization with a single library.
What are your thoughts? @vincerubinetti