Use the most recent release version of SCIFIO

The fix we rely on has made it into that version.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
NarHelper: nar-maven-plugin uses .jnilib on MacOSX, not .dylib

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
NarHelper: support launching from inside .jar files, too

Previously, we punted on finding the native library unless the
corresponding nar.properties were available via a plain file: URL. Now
we do better, we handle jar:file: URLs, too.

We still do not support unpacking the native library from a .nar file,
but expect the library to be available where the nar-maven-plugin
compiled it.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Read a .pgm instead of a .png

SCIFIO's .png and .jpg support relies heavily on ImageIO which in
turn relies on... AWT. Ergo: unsupported when running inside Avian.

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