VolumeData and various tweaks

src/apps/structure-info/density.ts

src/apps/structure-info/helpers.ts

src/apps/structure-info/index.ts

src/mol-data/db/column.ts

src/mol-io/reader/cif/schema/density-server.ts

src/mol-math/geometry/primitives/box3d.ts

src/mol-math/geometry/spacegroup/construction.ts

src/mol-math/linear-algebra/3d/mat4.ts

src/mol-math/linear-algebra/_spec/mat4.spec.ts

src/mol-math/linear-algebra/tensor.ts

src/mol-model/sequence/TODO

src/mol-model/volume.ts

src/mol-model/volume/_spec/data.spec.ts

src/mol-model/volume/data.ts

src/mol-model/volume/formats/density-server.ts