Add waffle chart type

[slowe]

Create a waffle chart type where we can:

• [x] set one or more values (as %)
• [x] set grid size (default to 10x10)
• [x] set a colour for each value
• [x] set grid symbol (default to squares but could be circles or custom icons)
• [x] set left-right direction

[slowe]

To resemble these examples from https://slidesgo.com/theme/waffle-chart-infographics

[slowe]

We will take the opinionated choice to fill up from the bottom.

[slowe]

More examples on the UK coronovirus dashboard https://coronavirus.data.gov.uk/

[slowe]

Waffle charts have been implemented.