Rework pom with BOM-style import and shaded jar

Replace parent stanza with dependencyManagement/import:
  -- requires explicit source/target JVM compile target
Change url to point to github repo.
Replace assembly plugin with shade plugin:
  -- removes packaging warnings
  -- also removes need for src/main/assembly/job.xml
Add git igore for reduced pom.
Replace 'provided' scope for flume-ng dependencies.