Allow access to tools native report formats

Makes it possible to generate phpcs, phpcpd, pmd, phploc and pdepend
native (XML) reports.

This feature is not activated by default.

Reports can be configured in .scrutinizer.yml. eg :

```yaml
    php_mess_detector:
        report:
            enabled: true
            dir: build/logs
            file: pmd.xml
```

Once activated, using the default configuration, reports go to :

* phpcs : build/logs/checkstyle.xml
* phpcpd : build/logs/pmd-cpd.xml
* pmd : build/logs/pmd.xml
* phploc : build/logs/phploc.xml
* pdepend : build/logs/jdepend.xml

The default configuration is compatible with
https://github.com/sebastianbergmann/php-project-wizard

This feature is fully backward compatible.