Refactor handling of multiple DVGeo objects with DVCon

[anilyil]

Description of feature

The PR #52 introduces a way to use multiple DVGeometry objects with a single DVConstraints object. So far, only @bbrelje uses these. There is a separate development of DVGeometryMulti that is used to handle intersecting components. I also implemented a similar functionality but in a different way. In that work, DVGeometryMulti class handles multiple component DVGeometries, and adjusts the naming for pyoptsparse etc.

Ideally we want to have a consistent implementation so both approaches can function together.

Potential solution

Around April 2021, we will refactor the pygeo code with @bbrelje to fix this consistency issue. At the same time, I will also merge the outstanding work in my development branch: https://github.com/anilyil/pygeo/tree/dev The main addition will be the DVGeometryMulti code, but there are other minor API changes for other pygeo classes.

[sseraj]

We merged DVGeoMulti in #113 but did not refactor the handling of multiple DVGeo objects with DVCon. I updated the issue title to reflect this.