Update version to 1.2.0-SNAPSHOT
Move to a new ChunkTask architecture

This allows me to add new tasks to the program, like changing block ids.
Use Java 7
Update NBT library

Update to NBT format of Minecraft 1.7:
- Doesn't care anymore about the number type
- All tags are now unnamed, except for the tags in a compound tag

Update code:
- All fields are now final
- TagType is no longer a byte, now a class