Refactor ProblemSolver

[tcreusc]

Current status: Restructuring Problem Solver classes

Main classes/functions: ProblemSolver, ProblemSolverFactory, ProblemSolverReducedDisp

Outline of the solution

• Restructuring ProblemSolver in different objects
• Redesign Reduced P.S. with Z matrix

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Assigned to: @gervilquin
Wingman: @RaulRubioSerrano