Add support for git LFS

Add support for git LFS to GitLab CE.

Feedback item.

Private issue.

TODO:

• Describe how GitLab(-shell) currently handles authentication on push and pull with binary files
• Describe how git LFS client-server work
• Explore existing implementations
• Discuss our needs(scaling, performance, disk usage, etc...)
• Implement

cc @jacobvosmaer @sytses @JobV @dzaporozhets