integrate Bootstrap UI + implement users sessions + implement a first backend for website data and sessions

Hello Felix,

Some times ago I fork your Awestats project and I modify/improve it for the needs of the company I work to.

Majors enhancements are:
* integration of Bootstrap for the web UI
* implementation of users sessions support with a first Mysql backend.
* implementation of website/users data storage using this backend too.

The code is ready to support other backends.
I also refactor the code structure a little.

It would be nice if you accept to merge these changes. After that we could combine our efforts for futur improvements on this project.

![screenshot_awestats](https://f.cloud.github.com/assets/606745/1623448/0afa222a-56b4-11e3-9375-aed79b77b6cc.png)

Regards,
Thomas Pierson