Fix the sender of the message

This patch fixes the sender of the message to WindowController showWindow method. It was previously set, erroneously, to nil.
Add basic support for Core Data

This patch adds some sort of basic support for Core Data usage through the whole application. It needs more code to be added, but the initial inclusion is there already.
Set a standard on initial comments

This patch changes all the initial file comments to follow the same standard. They were all different in content and format. Now there is a standard to follow when creating them, and all of them looks the same now, with the same required content.