Spritesheetpacking, minicore and noalpha for new hero/enemies/powers files

This commits processes the following files:

Avatar:
iron buckler female
iron buckler male

Enemies:
stealth

Powers:
bear_trap
caltrops
throw_axe
throw_knife

All those files (image and animation definition) were copied over to
minicore and processed there as well (resized of course).

The images were spritepacked and the animation definitions files
were updated accordingly.