Fixes #12364 - Use NPM+Webpack to handle external assets

This commit introduces NPM and Webpack to handle external assets.
It also provides ES6 support and a live reload dev server that can be
used by running `foreman start` instead of `rails start`.
Do not forget to run `npm install` before starting the server....

Fixes #16022 - Prevent stored XSS in host interface form

The host interface form may contain a stored XSS in the identifier field
allowing a user allowed to edit a host's interfaces to cause code
execution by another user viewing that host's edit form.

Fixes #15924 - Implement server groups and scheduler hints

Fixes #13768 - random and MAC-based name generator

Fixes #15996 - Multiple nav bars

fixes #3917 - replace protected_attrs with strong parameters

Filtering of attributes has moved from the protected_attributes gem to
strong parameters in controller concerns, to be in line with current
Rails recommendations.

Concerns are shared between UI and both API controllers and list the...

fixes #15829 - remove ace-rails-ap file modes from app.js

Also removes editor from precompilation list, it's in the main app.js
since fa8353d, and removes unused ACE extensions.

application.js has reduced from 2512 to 2381KiB.

Fixes #15037 - Improves editable elements in settings

Fixes #11749 - puppet env jquery selector more restrictive

This current jquery selector for puppet environment
selection would match any select box where name
included environment_id. This caused issues with
katello as we put a field containing lifecycle_environment_id...

fixes #14666 - support IPv6 in UI