Merge Navigator Plugin into Cytoscape.js

Navigator Plugin developed during GSoC 2013 by [bumbu](http://bumbu.ru) (Truhin Alexandr).
Right now you can view:
* [Documentation](https://github.com/bumbu/cytoscape.js/blob/gh-pages/src/plugins/jquery.cytoscape-navigator.md)
* [Bundled example](http://bumbu.github.io/cytoscape.js/navigator/)
* [Tests](http://bumbu.github.io/cytoscape.js/navigator/tests.html)