Tsurff merge

Description

Long overdue set of bug fixes for the Flux module (aka tsurff).
This include restart read/write and postprocessing utility otherwise unable to post process data for periodic systems but other minor bugs.
I have also added a set of tests to check ARPES in periodic system - a 2D system (1D periodic) to make it fast.

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.