add support for template_oid in the C++ SDK

[mejohnnaylor]

There are 2 approaches to this:

1) efficient but hard

• unless the inheriting parameter is written to (value, constraint) getValue and getConstraint use the referenced parameter to get these objects.
• once these are written to by setValue or setConstraint a local copy is maintained for future accesses.
• the ParamAccessor class will need to maintain "dirty" flags for all mutable objects in a Param. 2) inefficient but easy
• make a local copy of the referenced parameter

In no circumstances should the inheriting param overwrite the reference param.

[Isaac-Robert-Ross]

completed in PR #171, implemented using deep copies into the relevant param