Logging of training data about ergoface

[weinzmi]

tcx is hard to start with, so I try with csv
https://realpython.com/python-csv/

PROBLEM: maybe multi threading necessary for this to do not delay the loop for PWM
https://stackoverflow.com/questions/8241099/executing-tasks-in-parallel-in-python

PREREQUISITE:
#9 , otherwise, the code will get a mess

[weinzmi]

implemented in machine.py and watt.py
not happy with the solution, because it is wrapped too much inside the watt.py

the csv files are saved in folder "trainings"
every training gets a new filename with date & time.
looking forward to clean the code and add the name of the wattprogram to the filename

output:

TIME,POWER,CADENCE
20190104-075726,25,33.3
20190104-075727,25,33.3
20190104-075728,25,33.3
...