Add support for extensions

[lburgazzoli]

There should be new kind "extension" used to attach processors to a route:

- kind: "extension"
    name: "com.github.lburgazzoli.application.extension.beans.MyStep"
    properties:
      something: "ThisIsSomething"
      key1: "val1"
      key2: "val2"

The "extension" class should implement the following interface:

@FunctionalInterface
public interface SyndesisStepExtension {
    ProcessorDefinition configure(CamelContext context, ProcessorDefinition definition, Map<String, Object> parameters);
}