Check if constraints are satisfiable

[bertiqwerty]

The purpose of this would be to aid users by this consistency check when specifying constraints. Checking feasibility is only reasonably possible for linear constraints. To do this check we could try to solve a scipy.optimize.linprog problem.

[DavidWalz]

@Osburg this is something that is already done as part of reduce_problem.

[Osburg]

@DavidWalz but I think not necessarily for all constraints. For example linear inequality constraints that do not contain any of the eliminated variables just stay as they are and will therefore never be checked.