Band unfolding for arbitrary systems

Band unfolding will be performed as a post-processing tool for SIESTA. However, for general systems that do not comply with the restrictions mentioned in the blue print "unfolding1", specific outputs must be generated by SIESTA (this output requires an a priori knowledge of the translations corresponding to the approximate periodicity within the supercell, that should be specified in the input of SIESTA to generate a set of associated overlap matrices between displaced/equivalent orbitals in real space... well admittedly this explanation is not very clear, so you will be see it eventually...). Still, this should be a minor change for the code.