[ENH] Added messages with info about descriptors' range and number of iterations needed to optimize into ACSF Optimizer.

[FIX] Fixed terminationg condition in Nelder-Mead learning method and fixed messages both in N-M and Barzilai-Borwein GD.

[FIX] [ENH] Fixed ACSF parameter optimization. Iterative optimization used for the "preliminary network" training was replaced by Armadillo linear solver.