Add analytics to gem page

[lio-p]

ClickGems exposes a dedicated page per gem with detailed download analytics. It would make sense to link to the corresponding ClickGems page from each gem page.

For example, the utopia-analytics page, on RubyGems could link to its ClickGems page.

As an alternative, one or more charts from ClickGems could be embedded directly, since they support embedding.