Show charts on collection page

[php-coder]

When any user opens page with non-empty collection he should see 2 pie charts:

• by categories
• by countries

We should correctly handle cases when

• user has series with unknown countries (we should group them together and show in gray color)
• some of categories/countries represent less than 1% (we should group them together and show in gray color)

May be we could use Google Charts (https://developers.google.com/chart/) for that:

• https://developers.google.com/chart/interactive/docs/gallery/piechart#Example
• https://developers.google.com/chart/interactive/docs/gallery/piechart#donut