Fixed EZP-20438 - Provide an easy way to enhance available data in a view template

This PR adds a [generic listener to `ezpublish.pre_content_view` event](https://confluence.ez.no/display/EZP/Parameters+injection+in+content+views), bound to the template selection rules.

It allows to configure a content/location/block view the following way:

```yaml
#ezpublish.yml
ezpublish:
    system:
        my_siteaccess:
            location_view:
                full:
                    article_test:
                        template: AcmeTestBundle:full:article_test.html.twig
                        params:
                            my_service: @some_defined_service
                            osTypes: [osx, linux, losedows]
                            secret: %secret%
                        match:
                            Id\Location: 144
                    another_test:
                        template: ::another_test.html.twig
                        match:
                            Id\Content: 142
                        params:
                            foo: bar
                            some_hash: 
                                toto: tata
                                some: thing
```

Note that all configured parameters are only available in the template spotted in the template selection rule.