Added ColorExtractor

An alternative way to get block colors written in java.
Uses the new metadata feature.
Move ColorExtractor
Added option to create a single big image

Default is false.
Creates a single file image in the output directory.
Improved ColorExtractor and instructions

ColorExtractor prints the head comment of the block-colors file.
ColorExtractor prints hex numbers in upper case.
Removed dublicate Air entry.
Added several temporary fixes for unknown block colors.
Replaced default block-colors.txt.
Apply "Add" tag bits to block id

Can now load block ids higher than 255.