Remove drop shadow from badnik explosions, give drop shadows to Metal and flickies

Adds A_SetShadowScale to set an object's shadow scale, and A_ShadowScream which combines it with A_Scream, used for badnik explosions. Also gives BCZ1 Metal Sonic and the small animals their own drop shadows.

Fixes #218 (closed) and this old report: https://mb.srb2.org/threads/badniks-dropshadows-stick-around-for-the-explosion-frames.27851/