Make example input row not-optional

[MKaptein]

It is now optional to provide an example feature vector. We decided to make this a required argument (and off-course the test should pass).

Note:

• This affects the upload() function in main.py.
• We should change the tests to reflect this change.
• We should update the README.md accordingly.

[MKaptein]

Example row is now a required argument and is checked; if it fails it results in a "FATAL" warning and a stop of the upload progress.