ImageJApp conflates app name with net.imagej:imagej's TopLevelImageJApp

Firstly, we should rename it to `ImageJ2App`, to avoid confusion with the original ImageJ.

Secondly, when launching a SciJava GUI e.g. "swing" with imagej-common on the classpath, but not net.imagej:imagej, the ImageJApp reports the version as 2.0.4, which is the newest release as of this writing. But if you have net.imagej:imagej on the classpath, the TopLevelImageJApp (which should be renamed to TopLevelImageJ2App) takes precedence and it'll be 2.14.0.

This is *super confusing" especially because 2.0.4 and 2.14.0 are within the same ballpark and there is no indicator that in the former case, the 2.0.4 is the version of imagej-common, not ImageJ2 as a whole.