Show percentage of language detection on the language bar

Problem to solve

The bar shows an indication of which part is attributed to a language, but there's been interest in showing the actual percentage. This could be either in the tooltip, or another way.

Links / references

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/19480#note_101036920

Proposal

• Change language to font-weight: 600
• Add percentage in tooltip with color set to #bababa