#97 *.png as inputformat for icons

[Daniello Alto]

Well just tested JSmooth before and was happy that there beside ico also gif, jpg and png are allowed as inputfile for the exe icon.

Please add support for *.png as inputformat for Icons in Launch4j.

Offtopic: some other little thing I stumbled at first is:
Why do I have to set some path to a bundle JRE and the minium JRE version ?
I mean nice to know and to have it set, but in first place I should have the option to left this fields open/free since these settings are not absolutely necessary.