Integrate namespaces

This integrates namespaces in the installer and the three Fork applications. These are the reasons to do it:

* Avoid custom autoloaders
* Move to more standardised code
* Take a step closer to integrating other libraries (such as doctrine)

The installer and all frontend actions, widgets and ajax actions have been tested and work correctly
This is the list of all tested backend actions: https://docs.google.com/spreadsheet/ccc?key=0ApSZdWn75FMWdDBxVVlaaElEQVVySDN1VFFxUko1b2c#gid=0

Some actions weren't tested:

* Analytics: there's a bug in the core. Running the cronjob for getting data works when I execute the url manually. The curl call in the Loading.php action doesn't seem to work though (locally and in sneakers)
* Mailmotor: I don't have enough data to test some actions. I'll try to test this tomorrow

These are some bugs that are still available in the core of Fork (and that aren't caused by the namespaces)

* CommonUri removes greek (and probably other UTF-8) characters from url's. This should only be done when creating filenames, not url's
* Analytics: https://github.com/forkcms/forkcms/issues/629
* Analytics: the curl call to the getData cronjob in Loading.php doesn't seem to work (locally and in sneakers)