provide node path on configuration

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs? | No
| Applies to    | all
| Fixed tickets | 

If you no provide node path in assetic configuration, UglifyCssFilter throw a  `RuntimeException: Path to node executable could not be resolved.` 
The format that we use for the documentation is very strict for things like the length of the headings underlining. So please, reduce the underneath line length to match the length of the title. Thanks.