interactive camera axis helper

src/mol-canvas3d/camera.ts

src/mol-canvas3d/canvas3d.ts

src/mol-canvas3d/helper/camera-helper.ts

src/mol-canvas3d/passes/pick.ts

src/mol-math/linear-algebra/3d/vec3.ts

src/mol-model/loci.ts

src/mol-plugin/behavior/dynamic/camera.ts

src/mol-plugin/spec.ts