Ability to share a single CI configuration file for many repositories

Description

GitLab assumes every project repository has its own CI configuration file (.gitlab-ci.yml). This is flexible decision but not really effective in case you have dozens or even hundreds typical projects with basically the same CI script. The obvious workaround to have a copy of it in each rep is not working here because it will become not really maintainable, i.e. keep it in sync, do any little change etc.
It'd be perfect to have a way to share the same CI configuration file for many projects.

Proposal

Links / references

described workaround (in Russian) https://habrahabr.ru/company/flant/blog/340996/

Documentation blurb

Overview

Ability to share a single CI configuration file for many repositories

Use cases

While creating new project user can choose whether it should have it's own CI config file or it should refer to a common one

Feature checklist

Make sure these are completed before closing the issue, with a link to the relevant commit.