hector_pose_estimation_core: several updates (see below)

* Added missing orientation-orientation derivative in GenericQuaternionSystemModel
* Readded dimension paramters to SystemModel templates
* Readded class BaseState and State::base() accessors (currently unused)
* Added typed getters PoseEstimation::getSystem_<T>(name) and PoseEstimation::getMeasurement_<T>(name)
* IMU-based prediction is now in the GenericQuaternionSystemModel class again.
  The accelerometer and gyro models are added automatically if GenericQuaternionSystemModel::init() found an IMU input.
  GenericQuaternionSystemModel calls methods on the IMU model classes to get the errors, derivatives and noise.
  The IMU models themselves do not add
* Added class SkewSymmetricMatrix
* Avoid calling SymmetricMatrix::symmetric() as, surprisingly, this method seems to be quite expensive. Symmetry is only
  enforced if assigned from a matrix which is not a SymmetricMatrix.
* Added Eigen optimizations (avoid copies and added alignment macros)
* Moved system and measurement status management from class Filter to PoseEstimation