MixTest port

--HG--
rename : project.nmml => projectMix.nmml
rename : src-base/spine-libgdx/test/com/esotericsoftware/spine/MixTest.java => src-test/spinehx/MixTest.hx
SkeletonTest port

--HG--
rename : projectMix.nmml => projectMixTest.nmml
rename : project.nmml => projectSkeletonTest.nmml
rename : src-base/spine-libgdx/test/com/esotericsoftware/spine/SkeletonTest.java => src-test/spinehx/SkeletonTest.hx
SkeletonTest port