I re-added CorundumPlugin and CorundumListener and added to Block.

The CorundumPlugin and CorundumListener classes were made by me before,
but they were missing because of a glitch with Eclipse. Thanks to alexgryan
sending me his clone of the code, I got those classes back and I'm adding
them back to GitHub now. For now, these classes are still skeletal.

I also added some additional getters and setters to the Block class and
even a couple more to the BlockType enum.

Signed-off-by: REALDrummer <conman.davey@gmail.com>