Replace dataType with baseType+containerType to fix compilation error in AkkaHttpServerCodegen

[karolchmist]

Current version of scala-akka-http-server generator doesn't produce correct code if the response type is array. For example, for petstore it produces

def findPetsByStatus200(responseList[Pet]: List[Pet])
(implicit toEntityMarshallerList[Pet]: ToEntityMarshaller[List[Pet]]): Route =
   complete((200, responseList[Pet]))

This code is not valid because responseList[Pet] etc contains the type with brackets ({{dataType}} in api.mustache templates).

This PR fixes this by using {{baseType}}{{containerType}} instead, which produces:

def findPetsByStatus200(responsePetarray: List[Pet])
(implicit toEntityMarshallerPetarray: ToEntityMarshaller[List[Pet]]): Route =  
   complete((200, responsePetarray))

I had to change the type of complexReturnTypes from Set<String> to List<CodegenResponse>, which is necessary as far as I understand the code.

I'm not a Java developer, and it's the first time I use this project, so please let me know if something can be improved.

[HugoMario]

merged!!! thanks again @karolchmist !