New structures for Solutions & Results

[guimarqu]

Solution -> contains a formulation ref now

MoiResult -> to retrieve the result after solving a model with a MoiOptimizer/UserOptimizer

OptimizationOutput -> output of an algorithm & contains an OptimizationState

ObjValues -> contains incumbent bounds

OptimizationState :

    OptimizationState(
        form; feasibility_status = UNKNOWN_FEASIBILITY, termination_status = NOT_YET_DETERMINED,
        ip_primal_bound = nothing, ip_dual_bound = nothing, lp_primal_bound = nothing, lp_dual_bound = nothing,
        max_length_ip_primal_sols = 1, max_length_lp_dual_sols = 1, max_length_lp_dual_sols = 1,
        insert_function_ip_primal_sols = bestbound, insert_function_lp_primal_sols = bestbound, 
        insert_function_lp_dual_sols = bestbound
        )

A convenient structure to maintain and return solutions and bounds of a formulation form during an optimization process. The feasibility and termination statuses are considered as unknown by default. You can define the initial incumbent bounds using ip_primal_bound, ip_dual_bound, lp_primal_bound, and lp_primal_bound keyword arguments. Incumbent bounds are set to infinite (according to formulation objective sense) by default. You can store three types of solutions ip_primal_sols, lp_primal_sols, and lp_dual_sols. These solutions are stored in three lists. Keywords max_length_ip_primal_sols, max_length_lp_primal_sols, and max_length_lp_dual_sols let you define the maximum size of the lists. Keywords insert_function_ip_primal_sols, insert_function_lp_primal_sols, and insert_function_lp_dual_sols let you provide a function to define the way you want to insert a new solution in each list. By default, lists are sorted by best bound.

[vitornesello]

Is this structure still going to be completed? Right now it is not consistent with the description in the PR.
Why do we need it?