Re-added B-spline transformation for non-linear RT alignment in MapAlignerIdentification

Including updated tests.
we should explain what this actually means, from the spline library:

```
    /** 
     * Boundary condition types.
     */
    enum BoundaryConditionTypes
    {   
    /// Set the endpoints of the spline to zero.
    BC_ZERO_ENDPOINTS = 0,
    /// Set the first derivative of the spline to zero at the endpoints.
    BC_ZERO_FIRST = 1,
    /// Set the second derivative to zero.
    BC_ZERO_SECOND = 2 
    };  

```