Swagger Play2 module: add default values

It seems better to let swagger framework help us to determine something and generate some default values when they're absent.

So did some enhancement for swagger play 2 module:
- auto populate http method to operation based on route entry
- generate default nickname when operation's nickname is absent
- set it to 'string' when param's data type is absent

_And fixed some related test case errors._

Pls help review and give your suggestions.

**_And thanks for your excellent job! It's very helpful for my project. :)_**