Add Transform IO support for BSpline of order 1,2,4

By default ITK only registers BSplines of order 3, we manually
register additional bspline order to ITK transform IO factory.

Change-Id: Ia01890f8bc3ac09180c2a5c9c5ecc95ce1c2aeac
Addd BSpline::GetOrder method

Change-Id: I65b22213becc492df16b169844e8592df2c7ce58
Support creation of bspline of order 1,2,3,4

Adding new parameter to the constructor which takes the order. An
exception will be throw if the order is not supported.

Change-Id: Ia8b33300962824cad2be7392e3c04b501e3e25dc
Adding testing for bspline order

Change-Id: Ia03b229b57a007115e984cc11838a47f4a36e23f
Merge topic 'SIMPLEITK-573_AddAdditionalTransformMethods' into next

8e2d47b0 Adding testing for bspline order
3b00313a Support creation of bspline of order 1,2,3,4
ce470892 Addd BSpline::GetOrder method
2c44fb76 Add Transform IO support for BSpline of order 1,2,4