LUCENE-5404: Add .getCount method to all suggesters (Lookup), persist count metadata on .store(), Dictionary returns InputIterator, Dictionary.getWordIterator renamed to .getEntryIterator

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1565811 13f79535-47bb-0310-9956-ffa450edef68