borglab/gtsam: 4.2a5

Major changes since 4.2a4 inference module in wrapper moved SfmData classes from dataset.* to sfm folder lots of plotting/html/wrapping support for roboticsbook.org Detailed PR list Added inference module by @dellaert in https://github.com/borglab/gtsam/pull/1068 Added support for positioning in BayesNet plotting by @dellaert in https://github.com/borglab/gtsam/pull/1070 Wrap FindKarcherMean for Rot3 by @johnwlambert in https://github.com/borglab/gtsam/pull/1069 Wrapped more things by @dellaert in https://github.com/borglab/gtsam/pull/1077 Moved Sfm classes to their own files by @dellaert in https://github.com/borglab/gtsam/pull/1078 Expose some iSAM2/FixedLagSmoothing functionality for the bindings by @senselessDev in https://github.com/borglab/gtsam/pull/1053 Cleaned up loading SfmData by @dellaert in https://github.com/borglab/gtsam/pull/1082 Fixes to get matlab wrapper working properly by @varunagrawal in https://github.com/borglab/gtsam/pull/1083 Wrapper Update by @varunagrawal in https://github.com/borglab/gtsam/pull/1084 Add default constructor to PoseRotationPrior to fix serialization by @ScottMcMichael in https://github.com/borglab/gtsam/pull/1086 Add shared_ptr definition for remainder of camera objects by @dwisth in https://github.com/borglab/gtsam/pull/1088 Fix DotWriter wrapping by @dellaert in https://github.com/borglab/gtsam/pull/1089 Improvements in linear by @dellaert in https://github.com/borglab/gtsam/pull/1091 Frobenius Factor Eigen Fix by @varunagrawal in https://github.com/borglab/gtsam/pull/1096 New functionality in linear by @dellaert in https://github.com/borglab/gtsam/pull/109