remove dead code
Add ImmutableArray
add toDoubleBuffer and getElements for ImmutableArray
add BaseNDArray class
Make NDArray extend from BaseNDArray
Move fields and constructors from NDArray to BaseNDArray
lift shape-related code to BaseNDArray
lift IStridedArray implementation code
lift specialised getter functions
add INDArray.immutable() coercion function
sharpen immutable() methods for scalars