Add in-memory transpose and symmetric (undirected) graph construction for shared-memory apps.

[gurbinder533]

Expecting users to convert and pass the appropriate version of the graph such as transpose or symmetric for different analytics algorithms is very inconvenient.

We can amortize the cost of conversion by storing the transformed RDG.

[arthurp]

Random related issues: KatanaGraph/katana-enterprise#233, KatanaGraph/katana-enterprise#489. Also discussed here: https://github.com/KatanaGraph/katana-enterprise/issues/213#issuecomment-658393297. I found all this because I was looking for discussion I thought we had a while back. But I never did. Sigh.

We discussed tagging RDG versions as having specific properties and maybe even being derived from specific other RDGs. It should be integrated into the existing algorithms so they can avoid the documentation only assumptions of symmetry and the like. I think the result of the discussion was to push the idea back a bit and this may still not be the time to implement it fully, but I don't want to get it lost.

[arthurp]

We now have the in-memory operations to do this (d5dc5fb). However the algorithms don't use them, and don't have a way to know if they should use them. We will need to extend the graph metadata to include the needed information.