Throws a MissingRootTypeException instead of branching.

To DRY I removed branching in the `executeOperation` method and throws an error
whenever a query refers to a missing operation. This brings us a little closer to the
reference implementation https://github.com/graphql/graphql-js/blob/master/src/execution/execute.js#L419.

<T> javadoc fix up (graphql-java#815)

* More aggressive property look up

* <T> is for tea

Now follows spec as discussed

Fixes the copying of schemas and also the fact you cant set field vis…

…ibility on IDL schema creation runtime wiring (graphql-java#702)

(cherry picked from commit 12120e9)

bugfix: querytraversal should also work with mutations and subscriptions

add/fix javadoc

updated readme, delete readme.next

git ignore generated source folder

Merge pull request graphql-java#286 from dminkovsky/master

Updated README For v2.3.0

illegal global id should yield illegal argument exception