Changes

Bug 501424 - Generate equivalent pom.xml and category.xml

Adds an action to context menu on the Aggregation node (inside B3
editor), and a headless application, that generates a category.xml and a
pom.xml supposed to build
the model with Tycho.

There are a few differences in how versions are understood:
* b3 has versionRange; whereas category.xml hasn't
* b3 version (without range) is understood as a minimum version; in
category.xml it's exact version.

Change-Id: Iab99a3aa893559764a75e5024d227995c72f4419
Signed-off-by: Mickael Istria <mistria@redhat.com>