Work around ImageJ 1.x' sample image caching

Instead of just using Fiji's already well-tested sample image caching
plugin, ImageJ 1.x has its own, home-grown plugin. And even if Fiji
adds sample images to the menu that were around when ImageJ 1.x'
version of the sample caching plugin was written, it does not support
Fiji's sample images.

Therefore, we have not been given any choice but to override ImageJ
1.x' version of the plugin completely, it simply does not work
properly.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>