Configuration system refactor: documentation

Update the documentation according to the new Propel2 configuration system.
See pull request 527 on Propel2 repository https://github.com/propelorm/Propel2/pull/527

*Note*: I've added a new layout ("configuration") which is the same as "documentation", with a jquery-ui tabbed panel, to show the various formats of the configuration file.
This is a personal taste but I often find it weird to speak about an older version of Propel in the documentation. We are reading the documentation for the current version anyway so we could say, "Propel has support for Sybase ASE and MSSL server 2005 and above.". What do you guys think ? :-)