INT-3199: Fix inconsistency for candidate methods

JIRA: https://jira.springsource.org/browse/INT-3199

* Set `TypeDescriptor` to `Void.class` as default `targetParameterType` for falling-back
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