mol-plugin: refactor PluginComponent

src/mol-plugin/component.ts

src/mol-plugin/context.ts

src/mol-plugin/layout.ts

src/mol-plugin/state.ts

src/mol-plugin/state/animation/manager.ts

src/mol-plugin/ui/base.tsx

src/mol-plugin/ui/camera.tsx

src/mol-plugin/ui/controls.tsx

src/mol-plugin/ui/plugin.tsx

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

src/mol-plugin/ui/state.tsx

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

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

src/mol-plugin/ui/task.tsx

src/mol-plugin/ui/viewport.tsx