No more needed to use -i to disable icon padding

No more needed to use -i to disable icon padding

Now xmenu detects if a menu has an icon, and if it doesn't have, the
menu will not have the gaps fgor icons, making the -i flag unecessary
to disable the padding.   The -i option is still necessary, however,
to speed up xmenu loading, since it disables imlib2 initialization
routines.