Fixes some problems with HF and hybrid functionals with k-points

Description

Fixes some problems with HF and hybrid functionals with k-points

For some reasons some changes where made (sign change) which leads to a wrong current (non vanishing in the ground state). Also improves the calculation of the HF energy.

Some more testing is needed to have the correct energy.

News snippet

Fixes some problems with HF and hybrid functionals with k-points

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.

closes #650 (closed)