[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
Removed check for empty values
Change the way how Doctrine fixtures bundle is initialized & polish README file
Polish Behat DataContext file to improve performance
Moved backorders enabled to parameters.yml
Add support for n-number of database factories to easily be configured and used. This is important for being able to support custom ORM's
[payum] upgrade payum to 0.7. make it work
[payum] process sensitive values safely.
Delete old file
Add checks for finding a factory
- Update SyliusResourceBundle to add the default factories to the extension class. This was missed in the first commit
[payum] stable 0.7
Merge pull request #731 from isometriks/master

Removed check for empty values in ORM Repository
delete cascade variants when products are deleted
Merge pull request #758 from docteurklein/fix/534/delete-cascade-variants

delete cascade variants when products are deleted
Merge pull request #750 from formapro-forks/payum-upgrade-to-0.7

[payum] upgrade payum to 0.7
Merge pull request #734 from stloyd/bugfix/behat_datacontext

Polish Behat DataContext file to improve performance
Merge pull request #749 from Limelyte/multiple-database-factories

Ability to easily add factories to create configuration for different driver types
Typo fixed