[ENHANCEMENT] Refactored kernel structure

Refactored kernel structure.

````
app
├── AbstractKernel.php
├── AdminKernel.php
├── autoload.php
├── bootstrap.php.cache
├── cache
│   ├── admin
│   │   └── dev
│   └── website
│       └── dev
├── check.php
├── config
│   ├── admin
│   │   ├── config_dev.yml
│   │   ├── config_prod.yml
│   │   ├── config_test.yml
│   │   ├── config.yml
│   │   ├── routing_dev.yml
│   │   ├── routing.yml
│   │   └── security.yml
│   ├── config.yml
│   ├── parameters.yml
│   ├── parameters.yml.dist
│   ├── phpcr_doctrine_dbal.yml.dist
│   ├── phpcr_jackrabbit.yml.dist
│   ├── phpcr.yml
│   └── website
│       ├── config_dev.yml
│       ├── config_prod.yml
│       ├── config_test.yml
│       ├── config.yml
│       ├── routing_dev.yml
│       ├── routing.yml
│       └── security.yml
├── console
├── logs
│   └── dev.log
├── phpunit.xml.dist
├── Resources
│   ├── templates
│   │   ├── complex.xml.dist
│   │   ├── default.xml
│   │   ├── default.xml.dist
│   │   ├── example.xml
│   │   ├── example.xml.dist
│   │   ├── location.xml
│   │   ├── overview.xml
│   │   └── overview.xml.dist
│   └── webspaces
│       ├── sulu.io.xml
│       └── sulu.io.xml.dist
├── SymfonyRequirements.php
├── webconsole
├── WebsiteCache.php
└── WebsiteKernel.php

12 directories, 42 files
````
__Tasks:__

- [x] PHP Docs
- [x] Kernel parameter
- [x] Check if documentation needs updating
- [ ] gather feedback for my changes


__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | no
| Fixed tickets | -
| Doc           | -
@dantleech Would you really put that into the AdminKernel? If some parts of the API are exposed on the website also, this bundle will probably also be needed.