Refactor web to Silex microframework

Hello! This is a complete refactor of the web part to use the [Silex Micro framework](http://silex.sensiolabs.org/).

I was looking into adding feature like pagination and a way to display the line to input un the composer file for each version, and it would have been a litle hard to keep the code clean and organised. I decided to refactor it with silex, since the codebase already use composer and Symfony components, so that seemed the best tool to do the job. This will also pave the way to more features / optimization, like translations, more search criteria, etc...

That being said, I implemented the paging and the "paste this line to your composer file" options. Have a look at this screenshot:
![Search mode](https://cloud.githubusercontent.com/assets/923718/5532153/b90b617c-8a01-11e4-9320-1c6d550b8258.png)

Every parameters are easily customizable, if tweaking is needed. If you need more info on how to run it locally or on a webserver, this page has more details: http://silex.sensiolabs.org/doc/web_servers.html

Thanks!!