Implement sidre-to-conduit copies

[gunney1]

Summary

• This PR is a feature
• It does the following:
  • Implement Group::deepCopyToConduit and View::deepCopyToConduit
  • Support copying from one allocator id to another. The allocator ids are set before the copy, and the copy assures destination memory uses the right id.
  • Add tests for the new methods.

The goal of this change is toward supporting transparent switching between sidre and conduit. This is the state of conduit-sidre hierarchy copies, with this PR.