Fix for a number of PNG files for NESSY and Bruker icons for broken IDAT entries.
This problem was identified by Justin Lecher <jlec att gentoo doot org> in the post
http://article.gmane.org/gmane.science.nmr.relax.devel/4750 (Message-ID:
<5298572C.5010409@...>), or in the threaded view
http://thread.gmane.org/gmane.science.nmr.relax.announce/46/focus=4750.
As a result those icons are missing in the GUI. This was fixed using the pngcrush tool.