Rename mob source files to fit CamelCase.

Rename Cavespider.cpp to CaveSpider.cpp

Rename Cavespider.h to CaveSpider.h

Rename Magmacube.cpp to MagmaCube.cpp

Rename Magmacube.h to MagmaCube.h

Rename Zombiepigman.cpp to ZombiePigman.cpp

Rename Zombiepigman.h to ZombiePigman.h