ISPN-3950 Move KeyValueFilterFactory and ConverterFactory to core

* Moved to core/ to make it easier for users to implement factory
instances and avoid leaking server/hotrod components.
ISPN-3950 Reformat to 4 white spaces
ISPN-3950 Allow deployment of event filters and converters in server

* Adding filters and converters done dynamically now, to make it easier
to deal with deployments of these.
* An extension manager service has been created that handles addition
of Hot Rod servers and deployment of filter/converters. When new Hot
Rod servers are added, deployed filter/converters are installed in
them. When filter/converters are deployed, they're installed in all
known Hot Rod servers.
* Servlet deployment disabled for HotRod tests in server because it
forces deployment jars to be included within war. Instead, use JMX
deployment.
* Updated documentation to reflect how filter and converter instances
are plugging into Infinispan Server.