Use badge image template instead of using separate images

## What does this MR do?

Makes it possible to use template for badge instead of having multiple files.

## Are there points in the code the reviewer needs to double check?

We also have a deprecated badge in `controllers/ci/projects_controller.rb`.  We decided to leave it until 9.0, so we still have images in `public/ci/` until 9.0.

## Why was this MR needed?

We are going to implement build coverage badge, and we do not want to store 101 SVG images for each percentage value.

## What are the relevant issue numbers?

#3714

## Screenshots (if relevant)

![new_build_badge](/uploads/f1d4ed5e34278eb01f48994b5b0579f1/new_build_badge.png)

## Does this MR meet the acceptance criteria?

- [ ] ~~[CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added~~ (refactoring)
- [ ] ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- [ ] ~~API support added~~
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [ ] ~~[Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)~~ (refactoring)

See merge request !5520