Revamp support for building third-party apps via maven

- Publish onos-dependencies (autogenerated from deps.json). With most
  3rd-party dependencies listed as <dependencyManagement> to avoid
  version conflicts, and a minimal set listed as <dependencies> to
  simplify child poms. Similarly, we provide a number of plugins already
  configured as <pluginManagement> to support the whole life-cycle of
  apps (from build, to reporting and release).
- Update Maven plugins to work with JDK 11 (checkstyle, pmd, etc.)
- Publish onos-build-conf (with common checkstyle and pmd confs)
- Removed unused checkstyle code
- Fix OSGi version mismatch in deps.json to consistently depend on
  release 6 (the one supported by Karaf 4)
- Update/simplify archetypes to use onos-dependencies as the parent pom

Change-Id: Ic09b34e13fb49eb3d96df623b53a3617bbf7b7e4
diff --git a/tools/package/dependencies/empty.txt b/tools/package/dependencies/empty.txt
new file mode 100644
index 0000000..4c5974d7
--- /dev/null
+++ b/tools/package/dependencies/empty.txt
@@ -0,0 +1 @@
+This jar is intentionally left empty
\ No newline at end of file