Added new /convertallbo2 command

Added the /convertallbo2 command (BO2ConvertFolderCommand.java), which converts all bo2's in the given folder, and slightly changed the BO2ConvertCommand so I could use it as superclass for the BO2ConvertFolderCommand.

Compatible with TerrainControl 2.5, WorldEdit 5.5.8 and Bukkit 1.6.4-R0.1 (NOT below)

Creator13