Refactoring: controllers are now classes too

* Creating a Context class, containing all relevant information (current user, session, current url, current workspace)
* Creating a Controller class, the old procedural code belonging to the handleRequest method
* Adding a SPL autoloader, asks Smarty to stack its own autoloader

At this stage, we have now an engine offering a clean interface and ready to support applications.
Drop obsolete register_globals disable instruction

Support for this instruction has been removed in PHP 5.4.
http://docs.php.net/manual/en/migration54.incompatible.php

Obsidian Workspages current PHP version target is 5.4+.