Save repository size to projects table

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Merge branch 'repo-size-in-db' into 'master'

Save repository size to projects table

This will allow us to get largest repos by simple sql query.

Also it increase loading of `admin/projects` page a lot because right now it calculate 20x project sizes per page