* correct the Jacobian calculation of GravityFactor
* reimplement GravityFactor's analytical Jacobian
* adopt some minor changes from the GTSAM mainline
* use GTSAM's native AttitudeFactor instead of GravityFactor
* add missing header file and namespace prefix
* Removed GravityFactor. Fixed build with latest GTSAM version from source. Require c++17 when building with GTSAM>=4.3.0.
* Fixed cmake error when gtsam is not installed
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Co-authored-by: matlabbe <[email protected]>