configure.ac: quark-3.24 release

quark-3.23 release

quark.png: Shrink actual image

The change to using a GtkStatusIcon increased the size of the icon
significantly. The result now is the orignal image scaled to 42 pixels,
surrounded by transparency to fit the original 48 pixels.

The original image is now called "quark48.png", and is still used in the
"quark.desktop" file.

Initial quark-3.21 import