Converter: add warning when running with -jar instead of -cp

[selckin]

Prevents users like me wasting time

[apangin]

Accepting both -cp and -jar would result in even better user experience.
Instead of printing a suggestion, converter can do the trick automatically.

[selckin]

Accepting both -cp and -jar would result in even better user experience. Instead of printing a suggestion, converter can do the trick automatically.

Updated

[apangin]

I've merged PR with minor changes. Thank you for the contribution.