Revert "Removes unused constructor for NamedData."

This reverts commit 706ec114d48de7c060864ad8bc254a9c4da55f1d.
Adds Unit Tests for copy construction of NamedData & NamedVariantData.
Merge branch 'fix/nameddata-constructor' into 'master'

Fixes broken build due to deleted NamedData copy constructor.

re #9

+1: gsathyaseelan

Merged-on: https://www.assembla.com/code/OpenSurgSim/git/merge_requests/661013