Switch to HttpKernel

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no 
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | #1095
| Refs tickets  | 
| License       | MIT
| Doc PR        | 

The purpose of this PR is to switch to the [HttpKernel workflow](http://symfony.com/doc/master/components/http_kernel/introduction.html). This is an essential part of the equation because it allows us to use routing. The idea is Symfony HttpKernel will have a go at the request, and if not, Zikula legacy will take over.

There are no intended BC breaks here but a few things needed rejigging to make it work.