try to be a bit more clever in finding our libraries

try to be a bit more clever in finding our libraries

appending '..' to sys.path only works when seepark_web.py is started from
its directory, otherwise we get:

flask.cli.NoAppException: While importing "seepark_web", an ImportError was raised:

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/flask/cli.py", line 235, in locate_app
    __import__(module_name)
  File "/home/gregoa/src/toastfreeware/seepark/web/seepark_web.py", line 14, in <module>
    from seeparklib.openweathermap import openweathermap_json, OpenWeatherMapError
ModuleNotFoundError: No module named 'seeparklib'