Constrain of the guess magnetic density.

Description

Implementation of the possibility to impose the magnetic density for the first few iterations of the SCF cycle, based on the local magnetic moments specified by GuessMagnetDensities. This uses the Hirshfeld spin-resolved charge decomposition to define "atomic" densities from the total density, which are latter mixed to reproduce the local moments as defined by GuessMagnetDensity.

The merge request also fixes some problem with Hirshfeld (spinors and pseudopotential without density).

News snippet

Implementation of the possibility to impose the magnetic density for the first few iterations of the SCF cycle.

Checklist

• I have checked that my code follows the Octopus coding standards
• I have added tests for all the new features added in this request.