added JS paper elements, vulcanized

Create a new top-level directory for the `paper` package. This is a copy of the JS Polymer Core and Paper elements, vulcanized for use in chrome apps. From the readme:

```
A distribution of the Polymer Core and Paper elements.

This Dart package contains the JavaScript Polymer components without a Dart wrapper.
They can be used as is. The components have been vulcanized, so they are safe to use
in a CSP environment (such as Chrome Apps).

See http://www.polymer-project.org/docs/elements/ for more infomation.
```

@ussuri