Added x64 platform to MVSC solution.
Fixed #1.
Added missing reactive types to TypeTraits.h.
Added SetWeightHint and did some refactoring in the process:
* SetWeightHint is added as a member function to all reactive types.
* Moved NodeUpdateTimer to NodeBase.
* Got rid of domain specific registry. Instead, unique_ptrs to observers are stored per subject.
* Moved internals from Domain.h to DomainBase.h.
* Added common base classes for reactive types.
* Added some missing constructors & assignment operators & IsValid().
* Removed NodePtr() from public interface. Replaced by internal friend function GetNodePtr().
Added rudimentary test case for SetWeightHint.