I added some tests and story points because some of the tests require other classes that have not yet been wrapped (especially {{ExposureTable, which brings in a lot), and which have their own tests.

I merged the changes to daf_base after Pim Schellart [X] reviewed the pull request. I made the two changes requested by Pim: adding a bit to the new test and adding the test to master (requested on Slack) using DM-8581.

Wrap more of afw image and table

Wrap enough to enable the tests listed above.

WARNING: CoaddInputs is not properly wrapped: attempting to access
the "visits" or "ccds" fields will cause a segfault. I will create
a new ticket to address this issue; meanwhile one test
of testExposureTable.py is skipped for now to dodge it.

• Wrap afw::geom::polygon::Polygon
• Wrap more of Calib
• Wrap CoaddInputs but see warning above
• Wrap VisitInfo, including giving the constructor named arguments with defaults;
  this eliminates the need for makeVisitInfo, so reimplement that to raise
  a deprecation warning and then call the VisitInfo constructor
• Wrap a bit more of Wcs
• Wrap a lot more of Slots
• Wrap table::Exposure
• Wrap a bit more of Schema and Source
• Modify imageLib.py to import lsst.afw.table.io,
  thus allowing wrappers for image object that can be saved to tables
  to inherit from table::Persistable and support FITS I/O.

Looks fine, minor comments on PR.
The main question revolves about merging API changes with the pybind11 port. This can bite us in the end, although it is often unavoidable.

Thank you for the helpful review. All changes updated, rebased and merged.

I moved code that might help diagnose the CoaddInputs problem to a new branch u/rowen/debugCoaddInputs.