Add preview of Location object uses

I added the Location object and implemented it partially to SimpleDoor. At now the Location won't have World stored in it because I'm not sure is saving World object to Location safe to do. There is forum discussion about this feature: http://obsidianbox.org/threads/create-location-wrapper-like-the-bukkit-onee.22/

This commit also adds license header to SimpleBow because it didn't have it before I ran gradle licenseFormat