Koding Integration
## What does this MR do?
Will provide Koding integration with GitLab services. Forked from !4914.
## Are there points in the code the reviewer needs to double check?
I've introduced new layouts which might not be necessary, first time contributor.
## Why was this MR needed?
We're planning to ship Koding with GitLab.
## What are the relevant issue numbers?
#12759#14698
## Screenshots (if relevant)
### Screencasts
http://recordit.co/BDMbhwgxPDhttp://recordit.co/By0qiz1ClC
### Enable Koding in Application Settings
![image](/uploads/73a69421105c03aa2b0b47e2617d3fbc/image.png)
### Koding Dashboard
![image](/uploads/6c7dda34792280c0e4791e36af4eba11/image.png)
### Set up Koding Stack
1 - ![image](/uploads/d5c2b93f8e61b5cbffdb06f0267d485f/image.png)
2 - ![image](/uploads/44d9a9b574b8ac0c5eb553fb9653d5da/image.png)
### Run on Koding on Project Page
![image](/uploads/7d2b46221009074ffff75d66d5a1a555/image.png)
### Run in IDE on Merge Requests
![image](/uploads/65eed90c34c34b5fe7ad29ef9c717640/image.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)
- [x] 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)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)
See merge request !5909