Remove libraries that are not required for main vital_sqi functionality

[bahp]

Hi all,

I am trying to run an small example plot_read_signal.py. I have pulled the new vital_sqi version and it forces me to install the following library 'pyflowchart' in order to execute the script. However, my script has nothing to do with creating flowcharts. I think this 'non essential' libraries should be commented and only imported in those functions in which it is actually required.

Hope it helps!

Best