MD5 GPU vertex skinning

Added AnimationSkeleton class to serve as skeleton container for
BoneAnimationObject3D objects.

GPUSkinningMaterial extends PhongMaterial with vertex shader source
which calculates vertex positions
Update src/rajawali/animation/mesh/AnimationSkeleton.java

AnimationSkeleton is a container for BoneAnimationObject3D objects.

It calculates BoneMatrices by multiplying them with InverseBindPoseMatrices so that vertex bind pose positions can be used to calculate new vertex positions:

boneMatrix = boneTranslation * boneRotation * mInverseBindPoseMatrix

and 

position[i] = sum(weight[j] * boneMatrix[index[j]]) * bind_position
Update src/rajawali/animation/mesh/BoneAnimationObject3D.java

If GPUSkinningMaterial is used no calculations need to be performed.
Merge pull request #331 from CZdravko/master

MD5 GPU vertex skinning