Since rails 5 beta 2 support of petabytes and exabytes were added to the
`number_to_human*` methods.
See https://github.com/rails/rails/pull/22759
So for rails5 the comma separator gets shown for big numbers (EBs).
This adds counters for build artifacts and LFS objects, and moves
the preexisting repository_size and commit_count from the projects
table into a new project_statistics table.
The counters are displayed in the administration area for projects
and groups, and also available through the API for admins (on */all)
and normal users (on */owned)
The statistics are updated through ProjectCacheWorker, which can now
do more granular updates with the new :statistics argument.
