Add Avatar from author of the last commit to WebIDE status bar
Depends on: https://gitlab.com/gitlab-org/gitlab-ce/issues/46059
This is a follow up to https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/18756 (Issue: https://gitlab.com/gitlab-org/gitlab-ce/issues/44833). The avatar required backend development, so we're tackling it in this separate issue.