Bukkit

Converter and Bug Fixes
- Added a panel converter for v3 -> v4 panels. To convert panels, place them in a folder named `old_panels` next to the panels folder and type `/pa convert` to start the conversion. Note: the two versions are incompatible and you WILL need to modify the panels after converting them, this will just save you from doing most of the repetitive work
- Some bug fixes, inventory panels cannot be opened if they do not contain any items and fixed xp requirement tag
- Better example panels on folder generation have been added