Ship native libraries in ImageJ's lib folder

[ctrueden]

We currently pack the slim-curve native library into the curve-fitter JAR, then extract it using the SciJava Native Lib Loader at runtime. But ImageJ has a cleaner way of shipping native libraries: put the into the lib subtree beneath the correct architecture. If we did that instead, we would have fewer problems loading the native libraries at runtime (the java.library.path is already set) and we would no longer need the native-lib-loader dependency.

[dscho]

This is a perfect excuse to teach the imagej-maven-plugin about nar artifacts: imagej/imagej-maven-plugin#4