Add Vanilla js version

This is a try to make a vanilla js version.
I had to put your loader on a site that didn't use jQuery, and because the code was ready, i decided to send this PR.
I don't know if you will like this, the code its a bit ugly.

Anyway, tested in Chrome, Firefox and Opera.
And this suppose to work in IE 9+

The API is the same. The only difference is the way you call the main method:
```javascript
var preloader = materialPreloader(settingsObject);
preloader.on();
preloader.off();
```