getJacobianAndCovariance needs more explanation

[K0stIa]

Plase, clarify this.

Shouldn't this line of code https://github.com/dvorak0/VI-MEAN/blob/release/self_calibration_estimator/src/integration_base.h#L188 be something like this

L.block<3, 4>(3, 3) = 2 * Utility::Qleft(Quaterniond::Identity()).template bottomRows<3>();

basicaly similar to https://github.com/dvorak0/VI-MEAN/blob/release/self_calibration_estimator/src/integration_base.h#L195