wip snapshot interpolation proof of concept

src/mol-math/geometry/symmetry-operator.ts

src/mol-model/structure/structure/structure.ts

src/mol-plugin/index.ts

src/mol-plugin/state/actions/structure.ts

src/mol-plugin/state/animation/built-in.ts

src/mol-plugin/state/transforms/model.ts

src/mol-plugin/state/transforms/representation.ts

src/mol-state/transformer.ts