Create Vector, Matrix types and operations to enable linear algebra API

Survey of existing linear algebra libraries within mahout (samsara), spark (sparkML) and flink (flinkML) shows that they all expose local vector, matrix (sparse, dense) and distributed matrix types and operations. We should define these data types and operations within Beam and add this to the BeamML document https://docs.google.com/document/d/17cRZk_yqHm3C0fljivjN66MbLkeKS1yjo4PBECHb-xA/edit#heading=h.n51rhya8bv4f