Unnecessary buggy calls to MDL upgrade-/downgradeElements

These lines are present in several components originally present in the archive:

```
componentDidMount() {
window.componentHandler.upgradeElement(this.root);
}
componentWillUnmount() {
window.componentHandler.downgradeElements(this.root);
}
```

But "index.ejs" mentions that it is importing `react-mdl`:

```

```

which [does not require to call these manually](https://github.com/tleunen/react-mdl/issues/361#issuecomment-238843220). Moreover, it can hide errors happening in componentDidMount in child components, as pointed here: https://github.com/tleunen/react-mdl/issues/361.

I could remove the aforementioned lines without anything breaking in my app. Is this code present here on purpose, or should it be removed ?

Edit: These lines are useful only if you try to use MDL components without react-mdl or material-ui (which you probably shouldn't anyway).

Search the repository for componentDidMount/componentWillUnmount calls to componentHandler.upgradeElement and downgradeElements, then inspect index.ejs and the affected components. Confirm whether react-mdl already handles these calls and verify that removing them does not break the affected components or hide child component errors; done means the unnecessary calls are removed consistently.

Written by the indexing model from the issue text.