Fix indentation and imports
Add sources and javadoc plugins
Improve implementation of Composite Validator.

The previous implementation did always return the same
context. It should return the context as returned by
the validators iterated over.
Move validating function adapter to own package
Improve validating function adapter
Extract interface from validating function adapter
Inject validation builder into node methods
implementation
Change method signatureL return function that can
mutate nodes.
Change constructor access level to package
Introduce validating function interface
Added reposition node function and required validators
Use java 8 features
- default implementations in interface
- java.util.Optional (instead of Google's optional)
Use java 8 features
- Supplier from java instead of Google
- Predicate from java instead of Google where possible
Use java 8 features
- Predicate from java instead of Google
- No need for the functions anymore
Use java 8 features
- Predicate from java instead of Google
Introduced HippoItem, HippoProperty and HippoNode
Only classes under package traversal depend on Guava
Converted Streams into Lists
Reshuffle some methods
Formatting fixes