This PR contains the updates on the python bindings for substeps of IncrementalMapper and IncrementalMapperController. As a result, we are able to abstract a python pipeline as in the new example:
where the users (particularly from the research community) can play around with the logic in python and potentially iterate faster. Up to discussions on the naming of this example file python logic and on where to put it.
Ideally we can port the logic of BA with pyceres later such that one can construct customized problem, which can be potentially more friendly when integrating new features, sensors or the residuals from global sfm etc.