Package daybed.js for npm.js

Uses npm.js to package daybed.

It still misses a gulp rule of some sort to generate the daybed.min.js file that should be used by lib authors.
Can't we leave it as it was and call it on ``window`` instead of ``this`` ?

```
(function(exports) {
   "use strict";
    ...
    ...
})(window);

module.exports = Daybed;
```