OperatorEstBase DataLocality modes

[ye-luo]

Is your feature request related to a problem? Please describe.

1. Why OperatorEstBase::data_locality_ is not const?
2. Should OperatorEstBase::myName const and set via constructor?
3. SpinDensityNew implements copy constructor based on data_locality_ state but MomentumDistribution implements similar things in clone()

Please consolidate the design and add documentation.

[PDoakORNL]

I think 1 and 2 are probably correct. I'm working through my too clever copy constructor in 3 but I'm not sure that will put the logic in clone.