Pack spritesheet images (including minicore and noalpha)

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.

The images were spritepacked and the animation definitions files
were updated accordingly.
Merge pull request #261 from stefanbeller/master

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