js-template-component registers a custom tag rendered by js-template: each
<todo-list> below gets its own state from the context factory and its markup from
todo-list.tpl.html (*for, {{ }}, [(model)], *if, (click)).
Add a task (button or Enter), tick it, delete it with ×, clear the done ones -- then add and remove
whole lists to see the init / remove lifecycle hooks and the element methods.
Loading the module and the template...