Refactoring of the top level Cypher compiler and how it handles compatibility with older compilers
Introduces ExtendedExecutionResult

ExecutionResult is an interface that, by mistake, is what older compilers implement. Because of this, it
can't be changed in future versions. By introducing ExtendedExecutionResult and having compilers
produce internal ExecutionResults that are translated to the public interface, we preserve the ability
of changing the external interface without having to recompile old compilers.
Merge pull request #2774 from systay/new-execution-result

Update backward compatibility for Cypher