OGM-600 Establishing ForwardingGridDialect base class to facilitate the ...

...addition of further dialect facets and chaining them
Right, but `Contracts` feels like on exception to the rule. We use `Helper` more often. We even have a very desciptive `org.hibernate.ogm.massindex.impl.Helper` class :smiley:. 

I don't have strong opinion, Helper feels more in line with what we used in the project.
I don't like it very much actually, I think we could find better names in general.

I would like to include this pull request though and we can think of renaming the classes later eventually. @emmanuelbernard @gunnarmorling 
what do you think?,