Integrate automatic download of SD data in test_flights.py

[julienthevenoz]

-added 5 files from Denis' plotting code (all in the SDplotting subfolder of systemtests)
-added commands to enable/disable logging in the two example scripts (figure8 and multi_trajectory)

• modified test_flights.py to automatically download the SD data and plot it (using Denis' code)

I still have some recurring (and seemingly unrelated ?) bugs, documented in the "bugs" folder, which very often make the tests fail and prevent me from being 100% sure that this code works smoothly.

• Fixed crashing when trying to set a parameter that doesn't exist.
  Detail : if (crazyflie.py)setParam was called with a param that doesn't exist, keyError was raised which would crash crazyflie_server. For example in simulation there are no params initialized at all, so trying to set any of them would always crash. Solved this with a try-catch block which indicates logs an error but doesn't crash crazyflie_server

[whoenig]

Looks great thanks - just one small change needed.