Launch Site Descriptions, closes #9
Added descriptions to launch sites
 - Added new LaunchSiteExt to contain site descriptions (inherits from LaunchSite)
 - All LaunchDriver functions that returned LaunchSites objects now return LaunchSiteExt objects
 - LaunchSiteExt object held in static List
 - LaunchDriver is now initialised when the user enters an editor. Start() logic handles the default launch sites during first initialisation.
 - GUI code updated to handle LaunchSiteExt objects
 - GUI now has text area that displays site descriptions