Accept lazyset for a constant input

[mforets]

The "canonical" system type for BFFPSV18 algorithm is a ConstrainedLinearControlContinuousSystem with matrix A, identity matrix B, Universal set (or nothing ATM) or a lazyset for the constraints X, and finally a <:AbstractInput for the inputs.

For convenience, i believe that it is good if we accept (again, but this time using MathematicalSystems types!) a LazySet for the place of U constraint. However, i'm not sure where it would be a good place to make this preprocessing.

[schillic]

This algorithm-independent preprocessing of the model would be the first thing to do in solve. In the future there may be more preprocessing steps, so we should wrap this in a function (better even in a new file).