INT-3199: Fix inconsistency for candidate methods

JIRA: https://jira.springsource.org/browse/INT-3199

* Add a `Void` `TypeDescriptor` for methods without parameters
and leave it as `List` for case `canProcessMessageList = true`
* Change 'fall-thru; only to one method:
* Extract generic type from `Massage` parameter, so now
``` m1(Message<String> message);
    m2(String payload);
```
are equal by `payload type` and similar POJO causes ambiguity configuration exception