Ace ventura

## What does this MR do?

Makes Ace only load when it's actually necessary. The only two places it seems to be used is for Snippets and the File (Blob) Editor.

Before minification or compression, this takes the application.js down from 2.2MB to 1.6MB, and also removes two inline scripts :D

Compressed/Minified: master: 317KB/1.1MB, ace-ventura: 220KB/771KB

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

That this doesn't just completely break anything.

## Why was this MR needed?

Ace is a big library, this allows us to only load it when necessary.

## What are the relevant issue numbers?

#14372

## Does this MR meet the acceptance criteria?

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [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)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !4914