Ensure each component has a properly documented API

While most of our components have an API for programmatic usage, there's much we should do to improve things. In order of decreasing priority:
- Create proper reference documentation for API methods.
- Ensure method names and signatures are consistent across components.
- Ensure all major use cases are covered (`mdl-data-table` is missing important methods for adding and removing rows, for example).
- Add a factory method for every component, that knows how to build the DOM structure for a new instance of the component.