[T08] Port QuaternionEKF as the second estimator in wholeBodyEstimator.

[jeljaik]

Requirements

• [x] The robot-specific configuration file of wholeBodyEstimator will contain groups per each estimator in the module.
• [x] How do we want to specify which estimator will be instantiated by this module? more importantly, how to handle the instantiation of multiple estimators?

[jeljaik]

This task was bigger than expected, for this reason additional tasks were listed: https://github.com/robotology/codyco-modules/issues/153 https://github.com/robotology/codyco-modules/issues/155 https://github.com/robotology/codyco-modules/issues/157