- removed warnings
- added flake8 as CI target

- test run again
- notebooks not yet

- assignment collection
- sympyextensions

Modified the gitlab-ci for benchmarking purposes
Created a new Dockerfile for benchmarking purposes, which includes the
intel compiler.
Docker file now has likwid installed as well.
Created a machine file for the benchmarking machine.
Kerncraft updated and fixed.

TODOs:
    - cleanup of the yaml files
    - Test the Skylake machine file and kerncraft_coupling for correct
      behaviour

Updated testing of kerncraft_coupling and some functions in
kerncraft_coupling in order to be compatible with the kerncraft version 5.1

- pystencils can create now a non-compilable kernel that can be
  analyzed by kerncraft