3.0 Component, Behavior & Helper Configuration Improvement

With this approach it's also possible to configure Component, Behavoir & Helper in the app configuration. The configuration needs to look like the following:

```
'Component => [
    'Flash' => ['element' => 'Common.default']
]
```

Resolves https://github.com/cakephp/cakephp/issues/4296
I think in that case you would have to use MyFlash as key for the config settings. Better to use the actual "current" name. It would be too much overhead to also check all extending classes and their names IMO.