Allow interpolators to receive multiple components

[leouieda]

All of our interpolators except for VectorSpline2D can only receive a single data vector. We used the Vector interpolator to allow combining multiple interpolators to handle data with multiple components. But we're removing that class (#481). Instead, it would be more natural for all interpolators to allow multiple arrays in the data argument and then interpolate them all separately. We'd then need to store the model for each component and predict accordingly.