Enforce all actions to have a return value of Response

[MTDdk]

Currently when constructing actions developers needs to have the state of the response in mind at all times including eventual errors that might occur during execution.

This seriously makes the actions prone to errors or unwanted responses as it is not explicitly clear what and how the response is built.

By enforcing return values from actions, no response is implicit.
If 'void' is considered to be a valid return type, then a response 200 might be okay.
However, an enforced return value of 'Response' will also let the framework indicate, that a method actually is an action.

If the above is implemented it would also take of issue #13