added @with_request decorator to receive the request object as the first parameter

This PR adds a decorator `@with_request` which can be placed before service methods in order to receive the current request object as the first parameter.

This decorator is known from the XMLRPC module and should be available for JSONRPC as well

Example:

```python
def jsonrpc_method_without_request(self, arg1, arg2):
    ...

@with_request
def jsonrpc_method_with_request(self, request, arg1, arg2):
    ...
```