Update free_skymaps.adoc
Update free_skymaps.adoc

Cleaned up Gimp tutorial.
Split Blender part into chunks.
jMonkeyEngine/wiki.jmonkeyengine.org,jMonkeyEngine/wiki.jmonkeyengine.org,jMonkeyEngine/wiki.jmonkeyengine.org,jMonkeyEngine/wiki.jmonkeyengine.org