[cnc] added names for explosions

Easier-to-understand names for explosions, which can be used in the future. Can phase out old names/numbers slowly.
Also included some explosions from the C&C Content which were not in use and did not have names.
changing name of big_poof, for consistency

Changed "big_poof" to simply "poof". 

The word "big" will only appear if there are small, medium and large versions of the explosion.
Otherwise, it will just be "explosion" and "small_explosion".
Merge pull request #2670 from psydev/patch-47

[cnc] added names for explosions