Expand populate-app goal to also copy non-JAR resources #17

A Maven project such as imagej/imagej or fiji/fiji should be able to put scripts and other non-JAR resources somewhere (maybe src/main/scijava by default), such that they will get copied by the scijava-maven-plugin into an application installation when one is provided via the scijava.app.directory property.

Migrated from imagej/imagej-maven-plugin#11.