Revamp IIncrementalIngester API again for clarity and efficiency

git-svn-id: https://svn.apache.org/repos/asf/manifoldcf/branches/CONNECTORS-1118@1644386 13f79535-47bb-0310-9956-ffa450edef68
Convert deletion methods to also cut back on loading of instances

git-svn-id: https://svn.apache.org/repos/asf/manifoldcf/branches/CONNECTORS-1118@1644390 13f79535-47bb-0310-9956-ffa450edef68
Remove unused reference

git-svn-id: https://svn.apache.org/repos/asf/manifoldcf/branches/CONNECTORS-1118@1644391 13f79535-47bb-0310-9956-ffa450edef68
Pull up further refactorings related to CONNECTORS-1118 from trunk.

git-svn-id: https://svn.apache.org/repos/asf/manifoldcf/branches/release-2.0-branch@1644400 13f79535-47bb-0310-9956-ffa450edef68