Requirements update and setup.py change

[a-capra]

My apologies: this is not a well-organized PR.
My system is:
CentOS Linux release 7.9.2009 (Core)
Kernel: 3.10.0-1160.11.1.el7.x86_64
gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-44)
Python 3.6.8

• additional requirement: pyYAML is required otherwise the jupyter notebook doesn't run;
• deperecation of pyYAML loader;
• exception handling in setup.py otherwise pip install -e . doesn't work, however I'm not sure whether this fix
  reflects the intended behaviour.