Add badges or status indicator to language details pages

[David Planella]

Right now the language details pages (http://91.189.93.77/stats/quantal/ca) are useful for translations teams to see a breakdown of coverage for each app, but they don't show the overall coverage figure other than in the graph.

It should be shown on the page, preferably as a badge, e.g.:

- Supported: coverage figure over 80%
- Good: coverage figure over 70%
- Average: coverage figure between 50 and 70%
- Poor: coverage figure below 50%