XML indentation with environment support

Complements #612 

This is a draft to get more suggestions. With this pull request I added a support to `indented` method to get a value from environment as discussed in #612.

Since this change affects `MockSerializationResult`, the constructor was deprecated and a new constructor with `Environment` parameter was added to keep compatibility backwards.

After this pull request, we can add the same support to JSON serialization.

Docs will improved before merge.
https://github.com/caelum/vraptor4/blob/master/vraptor-core/src/main/java/br/com/caelum/vraptor/environment/DefaultEnvironment.java#L77-L79