make self.population uniform and consistent

[mmckerns]

self.population is not uniform and consistent for each solver, and also for the population initializer methods.

For example, SetInitialPopulation can produce a population which is a nested list of lists, except for population[0] which in an array. This is different from SetRandomInitialPopulation, which produces a nested list of lists everywhere. This is transferred to self.population, and not corrected before the main part of the solver algorithm. The solver algorithms should choose to use arrays or lists, but an arbitrary combination of both is not good.

[mmckerns]

population generators made uniform (nested list of lists) in r636