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 #15924 - Implement server groups and scheduler hints

Fixes #13768 - random and MAC-based name generator

fixes #15919 - statistics page is loaded via AJAX

Also:
- refactor how statistics data is being called, now it should be trivial
to add additional charts or consume other data from it. It should make
it much easier to reuse statistics charts in other places...

Fixes #7955 - /apidoc should point to v2 documentation by default

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 #15863 - add short session or request ID to logs

New middleware stores the session and request IDs (either from
X-Request-ID or a UUID generated by Rails) in the logger's thread
storage. The truncated session ID is now logged by default to minimise...

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 #15751 - replace spork with spring in development

To make use of it, run bin/rails and bin/rake rather than plain
rails or rake commands, and run `spring status` or `spring stop` to
check and stop current background processes.

Test log removal has moved to the logging framework as the file would...