[Feature] [API] export repo-language info

[6543]

since #8037 created LanguageStat's for each repo ... get this info via API too

[6543]

github has:

• https://developer.github.com/v3/repos/#list-languages
  and export main language via "language": null, json enty on repo-responce

[lafriks]

It's not really possible to do that currently as bytes for each language are not really saved to database only percentage

[lunny]

Why not that API display number of files or lines but bytes? Is that meaningful?

[lafriks]

Because percent is calculated without loading all file from git, just by detecting file size so that is faster as to detect line count