Load neutralconfiguration from srdf for joint.nq()>1 (#652)

* [parsers][srdf][neutralConfiguration] Update verbosity. If found, display joint and value. If not found, display error message. Don't display both.

* [parsers][srdf][neutralConfiguration] remove ambiguity in name of xml tag and pinocchio::Joint joint instance

* [parsers][srdf][neutralConfiguration] Load q0 value for joints with nq>1

* [srdf][unittest][neutralConfig] Add joint state to simple humanoid

* [srdf][unittest] Use simple_humanoid for loading q0.

* [srdf][neutralConfiguration] remove scalar parsing for nq()==1. Simplify Eigen::Map template