Merge branch 'es6it' into 'master'

Add es6 gem

## What does this MR do?
Add ES6 to ES5 compiling via Babel and the sprockets es6 gem.

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

## Why was this MR needed?
So we can write ES6

## What are the relevant issue numbers?
https://gitlab.com/gitlab-org/gitlab-ce/issues/20098

## Screenshots (if relevant)
![Screen_Shot_2016-07-25_at_10.56.02_AM](/uploads/04ceeedb8235fd3a7601bc4bece313a8/Screen_Shot_2016-07-25_at_10.56.02_AM.png)

![Screen_Shot_2016-07-25_at_10.55.54_AM](/uploads/163c46a3d878924ab1717fccca468003/Screen_Shot_2016-07-25_at_10.55.54_AM.png)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [x] All builds are passing
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] 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)

See merge request !5473

CHANGELOG

@@ -9,6 +9,7 @@ v 8.11.0 (unreleased)
   - Make fork counter always clickable !5463 (winniehell)
   - Load project invited groups and members eagerly in ProjectTeam#fetch_members
   - Add GitLab Workhorse version to admin dashboard (Katarzyna Kobierska Ula Budziszewska)
+  - Add ES6 gem
 
 v 8.10.2 (unreleased)
   - User can now search branches by name. !5144

Gemfile

@@ -9,6 +9,7 @@ gem 'responders', '~> 2.0'
 # Specify a sprockets version due to increased performance
 # See https://gitlab.com/gitlab-org/gitlab-ce/issues/6069
 gem 'sprockets', '~> 3.6.0'
+gem 'sprockets-es6'
 
 # Default values for AR models
 gem 'default_value_for', '~> 3.0.0'

Gemfile.lock

@@ -85,6 +85,10 @@ GEM
       faraday (~> 0.9)
       faraday_middleware (~> 0.10)
       nokogiri (~> 1.6)
+    babel-source (5.8.35)
+    babel-transpiler (0.7.0)
+      babel-source (>= 4.0, < 6)
+      execjs (~> 2.0)
     babosa (1.0.2)
     base32 (0.3.2)
     bcrypt (3.1.11)
@@ -700,6 +704,10 @@ GEM
     sprockets (3.6.3)
       concurrent-ruby (~> 1.0)
       rack (> 1, < 3)
+    sprockets-es6 (0.9.0)
+      babel-source (>= 5.8.11)
+      babel-transpiler
+      sprockets (>= 3.0.0)
     sprockets-rails (3.1.1)
       actionpack (>= 4.0)
       activesupport (>= 4.0)
@@ -963,6 +971,7 @@ DEPENDENCIES
   spring-commands-spinach (~> 1.1.0)
   spring-commands-teaspoon (~> 0.0.2)
   sprockets (~> 3.6.0)
+  sprockets-es6
   state_machines-activerecord (~> 0.4.0)
   sys-filesystem (~> 1.1.6)
   task_list (~> 1.0.2)