no more crashes on wrong input

v1.1

fixed crashes on wrong input, now we give a message

v1.0

There are 2 versions: in English and in Russian languages.

phase_plane_helper.en.2015.03.28.7z is with English labels (description is here)

phase_plane_helper.ru.2013.07.02.7z is with Russian labels.

English version contains automatically generated tasks. There are no technical differences in the code.