Add simple documentation for methods without bodyParam

post, put and patch requests without a bodyParam will now be documented
with an undocumented bodyParam. This will allow people to try out this
undocumented field in the Swagger documentation in the admin interface.
Merge pull request #874 from triAGENS/foxx-doc-generator-improvements

Foxx API Documentation explorer doesn't show POST/PUT/PATCH bodies without bodyParam