CASA 6.1

[teuben]

Although casa6.1 is out, it will be a parallel effort to ensure the scripts work under CASA6. In this issue we plan to track those, but for the forseeable future casa 5.6 and 5.7 ( just came out) are going to be used.

[teuben]

we decided to do python3only a while back. The branch with that name is going to be the branch to test this, and will become the master/main branch