added ParamDefinition.isHidden, various mol-plugin tweaks

src/mol-plugin/command.ts

src/mol-plugin/command/base.ts

src/mol-plugin/command/camera.ts

src/mol-plugin/command/state.ts

src/mol-plugin/index.ts

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

src/mol-plugin/state/transforms.ts

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

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

src/mol-plugin/ui/controls/parameters.tsx

src/mol-plugin/ui/state/common.tsx

src/mol-util/param-definition.ts