Updated Persist writer to have a configurable background flush thread
Updated termination process
Fixed deadlock issue
Fixed issue where exception terminated thread and it wouldn't start again
Merge remote-tracking branch 'origin/pr/7' into streamstutorial

Conflicts:
	streams-contrib/streams-persist-elasticsearch/src/main/java/org/apache/streams/elasticsearch/ElasticsearchPersistWriter.java
	streams-contrib/streams-persist-elasticsearch/src/main/jsonschema/org/apache/streams/elasticsearch/ElasticsearchWriterConfiguration.json
was missing imports and using random in a way that wouldn't build in jdk6