docker: install submodules in editable mode
docker: install submodules in editable mode

closes reanahub/reana#236

reanahub/reana-job-controller,diegodelemos/reana-job-controller,reanahub/reana-job-controller,tiborsimko/reana-job-controller,tiborsimko/reana-job-controller,diegodelemos/reana-job-controller