[FrameworkBundle], [DependencyInjection] added logging of unused tags

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #11511
| License       | MIT
| Doc PR        | -

I gave this a short shot and added a new CompilerPass to log all tags, which are not queried by ``ContainerBuilder::findTaggedServiceIds()``. 
Example log:
````
[2014-08-23 15:45:32] app.WARNING: Tag "kenrel.event_listener" was defined on the service(s) foo.bar_service, but was never used. Did you mean "kernel.event_listener"
````

This is maybe not the best solution, for tags defined in optional bundles. So I added a ``ignore`` configuration option for this case.

Configuration:
```yaml
framework:
    compiler:
        validate:
            tags:
                enabled: true
                ignore:
                    - foo.bar
```

A better approach could be a explicit declaration of the tags and their arguments? Maybe in the extension class of the regarding bundle? But what should happen when a 3rd party bundle doesn't add such declaration?


`array_unique()` doesn't modify passed array