All of the icons are square, only providing the size in one direction is
enough. This change lets us avoid some unnecessary complexity in the
Makefile.
Apple requires a different set of icons now-a-days. This change involves
removing the 76x76 icon and adding icons with the following sizes;
40, 58, 80, 87, 167 and 180.
It is not a launcher icon, but rather used for display on Google
Play. As such it is not needed and removing it mitigates the issue
of some buggy browsers downloading each and every listed icon.
