Use CS version of lib. Normalized to forked package structure

@vendasta/va @ywang-va @dhopkins-va 

I'm not sure how valuable this will be to review but here it is anyways.

This PR updates the forked version of MR to be the repcore version. The biggest change is that the newer version relies on cloudstorage rather than the Files API for the _ReducerWriter which breaks a lot of unit tests in Core. The newer version also extracts some additional files out into individual modules (but leaves duplicate code for each of them so I'm not sure if this was intentional).