EMI: Don't set global alpha to 0 when light mode is set to LIGHT_NONE.

Fixes sprites not appearing in various places. For example the lights on Stan's house now show up.
EMI: Read vertex color values from sprb files.
EMI: Draw model faces with alpha textures also to the depth buffer. Fixes #874
EMI: When a chore is stopped, remove it immediately from the list of playing chores.
EMI: Sprite drawing fixes for OpenGLS renderer.
EMI: Read depth write and alpha test flags from sprite files.
EMI: Obey dim level also when drawing sprites.