ISPN-4900 Split-brain: cancelled ST results in missing data

Reset the rebalance confirmation collector when entering degraded mode
ISPN-4934 Upgrade to protostream-2.0.1.Final
ISPN-4925 Enhance documentation on Spring Integration
ISPN-3938 AdvancedAsyncCacheLoader.process() concurrency issues

Simplify ExecutorAllCompletionService to track the tasks itself instead of
using an ExecutorCompletionService.