Adds JavaScript validation for group path editing

## What does this MR do?

- Prevents group_edit form submission when special characters are included in the new group name
- Enhances gl_field_errors to support this use case and be more re-usable. 

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

**The implementation of validation is here: https://gitlab.com/gitlab-org/gitlab-ce/commit/73d997046cac376ccdbcaac6f183002bc19b9a1f**

The rest of the diff for this MR is augmenting gl_field_errors

## Why was this MR needed?

- Currently we allow submission and a 500 error is returned. 

## Screenshots (if relevant)
![2016-10-21_14.11.21](/uploads/2bef5764d3f2429dd0f900661153eef7/2016-10-21_14.11.21.gif)
## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG.md) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [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 it does - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/23564, https://gitlab.com/gitlab-org/gitlab-ce/issues/19756, https://gitlab.com/gitlab-org/gitlab-ce/issues/19736, https://gitlab.com/gitlab-org/gitlab-ce/issues/23922

See merge request !7041