fix media component

turns out the proper Polymer way to do this is to use `<link rel='import' href='popcorn.html'>`, and create a popcorn.html file that simply contains these three script loads, so
```
<script src="popcorn.min.js"></script>
<script src="popcorn.wrappers.min.js"></script>
<script src="popcorn.modules.min.js"></script>
```
That way polymer will treat it as a "real" dependency