Split core ImageJ commands into two components

From an [imagej-devel mailing list thread](http://imagej.net/pipermail/imagej-devel/2013-May/001495.html):

> Are you planing to re-organize the plugins, e.g. such that plugins,
> which are interesting for any application reside in their own
> jar-file?

The idea is to split the core IJ commands into two different components (i.e., JAR files): one intended for headless consumption, and one intended for the end user application (which will include e.g. the interactive meta-commands).

Migrated-From: http://trac.imagej.net/ticket/1953

Start by reading the linked imagej-devel mailing-list thread and inspecting how the core IJ commands are currently organized. Define the boundary between headless commands and interactive meta-commands, then verify that the result produces two separate JAR components with the intended contents.

Written by the indexing model from the issue text.