Implement continuous reconnection to cassandra cluster

Closes-Bug: #1273282
Change-Id: Ieae6e4665e6f318f5b357fe33985845882be2ff4
Merge "Implement continuous reconnection to cassandra cluster"
Adds documentation from docstrings

Adds documentation from docstrings to Developer Guide

Change-Id: If01af0145efc1bd0695eca673429b42bee4d9001
Implements: bp magnetodb-documentation
Disable data item level operation events for message queueing.

Changed data level notification to DEBUG queue. If rpc notifier is used,
disable notification for DEBUG events.

Change-Id: I0476805fbce5e7ac2e000a011e0dea08a661b1ac
Implements: blueprint event-aggregation
Merge "Disable data item level operation events for message queueing."