Fix to loading and new PlotWorldLoadEvent

- Fixed an error when loading because the saveNextFreed was trying to
save a non-existent world
- Added a new event for when a plotworld is done loading
Merge upstream/master into development

Conflicts:
	src/main/java/com/worldcretornica/plotme_core/PlotMapInfo.java
	src/main/java/com/worldcretornica/plotme_core/PlotMe_Core.java
	src/main/java/com/worldcretornica/plotme_core/SqlManager.java
	src/main/java/com/worldcretornica/plotme_core/event/PlotMeEventFactory.java
	src/main/java/com/worldcretornica/plotme_core/listener/PlotListener.java