Add TableCollection.sort options for individual_start etc

[jeromekelleher]

We are missing ways to control the sorting process in Python, which is needed in particular for preventing individual sorting from changing parent references (#1653).

We should be able to add individual_start, migration_start etc options directly to the Python API and let the C API handle errors when we don't support the functionality.

[jeromekelleher]

See also #1475

We probably shouldn't put in the individuals, though, since we don't sort them now.

[jeromekelleher]

Was this closed by #1826 @benjeffery?

[benjeffery]

#1826 added sites and mutations, not the full set as suggested here. I think this can be closed though as the spirit of the issue has been solved.