Enforce SciJava annotation processing even in Eclipse

With this topic branch merged, `pom-scijava`based Maven projects will be built properly even in Eclipse (which is slightly challenging due to Eclipse's ignoring of annotation processors).

This PR relies on https://github.com/scijava/scijava-maven-plugin/pull/2 (therefore, the latter PR should be merged, and `scijava-maven-plugin` version `0.2.0` released, first).