added support for parsing hash on vector elements (#4502)

* added support for parsing hash on vector elements

reversed check for scalar to check for vector

added C++ generation of cpp_type vectors

removed ctor call for vector fields
added condition !vector for cpp_type check

added Pack() and UnPack() code generation for vector of hashes

* schema change:
added table Referrable and weak references towards it from Monster

added single_weak_reference to Monster table
changed order with vector_of_weak_references

* re-generated monster schema dependent code

added Referrable.cs to FlatBuffers.Test.csproj