The Netty version set by Spring IO platform's BOM is not compatible with
netty-socketio.

Additionally, made first use of it in CouchDBDao.

This will allow us to use type annotations, lambdas, etc. Documentation
already states Java 8+ as a requirement.

Bulk deletes run by periodic clean ups might fail when run for the first
time or after and there are a lot of documents accumulated

Lists of documents for deletion are now partitioned into sub lists with
a maximum of 500 elements using Google Guava.