[WIP] Adopted template overriding from other actions like update

Currently when you use the `SyliusResourceBundle` standalone, when you want to override the template for the delete action you have to define it this way:

``` yaml
my_delete:
    pattern: /my/{id}
    methods: [DELETE]
    defaults:
        _controller: my.controller.my:deleteAction
        template: MyCoreBundle:My:delete.html.twig
```

This is inconsistent with the other actions. This PR changes this so that it works with the folloging syntax:

``` yaml
my_delete:
    pattern: /my/{id}
    methods: [DELETE]
    defaults:
        _controller: my.controller.my:deleteAction
        _sylius:
            template: MyCoreBundle:My:delete.html.twig
```

Before merging this PR we should reconfigure the routes so that `SyliusWebBundle:Backend/Misc:delete.html.twig` will be used again ;-)
Configured template for all delete actions
Change the way how Doctrine fixtures bundle is initialized & polish README file
Moved backorders enabled to parameters.yml
Consider shipping category during method eligibility check
Apply core review feedback
Merge pull request #776 from Richtermeister/shipping-category-check

Consider shipping category during method eligibility check
Update phpspec
[CartBundle] Fix cart bundle spec & few fixes for README file
[InstallerBundle] Fix spec to work with newest phpspec
[InstallerBundle] Fix README file
Merge pull request #784 from stloyd/bugfix/cart_spec

[CartBundle] Fix cart bundle spec & few fixes for README file
Merge pull request #785 from stloyd/bugfix/installer_spec

[InstallerBundle] Fix spec to work with newest phpspec
Adjust README files along all bundles
[ci skip]
Redirect to specific URL after add to cart.
Refresh cart right after cart_change event
Merge pull request #788 from kayue/patch-1

Redirect to specific URL after add to cart.
Merge pull request #786 from stloyd/bugfix/readme_adjust

Adjust README files along all bundles
Optimize order page and handle deleted products
Merge pull request #792 from Sylius/order-integrity

Optimize order page and handle deleted products