QEHeat code to compute energy current with QE

This is the code that computes the energy current as described in the paper

Marcolongo, Umari, and Baroni, Nat. Phys. 12, 80 (2016)

All the technical details about what is computed are explained in

Marcolongo, Bertossa, Tisi and Baroni https://arxiv.org/abs/2104.06383 (2021)

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At the moment there are no modifications to the QE code (*edit: see discussion below), and the code is as independent as possible, only a folder is added. (I still need to modify the main Makefile and the cmake related build system, and more integration can be done) There are tests that can check if something breaks the code. All main features are tested. The documentation is written with the QE tools. The executable that this code builds is called all_currents.x and it computes (for gapped systems) energy current, electronic density current and mass currents in some documented output file. The code is a post processing tool that runs some pw and some LR routines along a cp.x trajectory.