SemialgebraicComplex Improvement

[ComboProblem]

Add method to semialgebric complex given input of a region type returns a list of cells with given region type.

[ComboProblem]

Something like
sage: clx = SemialgebraicComplex(family_of_functions, parameters)
sage: clx.bfs_compeltion()
sage: extreme_cells = clx.get_region_list(region_type_name="is_extreme")
sage: extreme_cells
[a list of all cells that are extreme here]