Scaled DataContainer

[paskino]

Oftentimes we multiply a DataContainer by a scalar. In ScaledFunction every invocation of almost every method requires a multiplication of a DataContainer by the scalar in the ScaledFunction.

@gfardell suggested we could save some computation by storing the scalar in the DataContainer rather than perform the multiplication, and perform the multiplication only when required.

This seems to be of particular interest in case of ScaledFunction and ScaledOperator

[paskino]

We should get an example and see how we could benefit from this change.

However, I believe that concrete Function classes should not use ScaledFunction when multiplied by a scalar but deal with that by themselves, e.g. LeastSquares has a parameter c, so we could be redefining the multiplication on the left to return another LeastSquares with the constant c multiplied by the scalar instead of returning a ScaledFunction.

Similarly, concrete operators could be dealing with the scalar multiplication internally rather than defaulting to the ScaledOperator. ScaledOperator or ScaledFunction are still relevant in case we add new operators or functions.