Replace the current backend based on wbfs_file with a brand new backend based on wit.

Although Wbfs_File is a highly functional tool and it perfectly serves for our purposes, it has some drawbacks. E.g., I don't know if its currently maintained or not, and its source code is rather dirty and caotic. In order to continue the development of Yawf and implement some new features, it would be a great idea to switch from Wbfs_File to another tool. Perhaps the most promising choice is Wit (http://wit.wiimm.de/), which has the same features than Wbfs_File and is updated more often.