CASA 6.x installation

[drtobybrown]

Since CASA versions >=6.0 can be called from within standard python scripts, we need a method for the user to specify which version of casa they want to call.

We can test how best to do this with CASA 6.1 but if it's easy then what about casa610?

[yeunga]

6.1 related installation work in issue opencadc/science-platform#99 has been moved to this issue.

[drtobybrown]

The pip wheel install of casa 6.1 requires python 3.6 so we’ll need to have that kernel for a demo.

[drtobybrown]

Possible solution could be combined with #44

[brianmajor]

Yes, possibly a new kernel, or, a new casa focussed notebook-server with casa 6 and other required software pre-installed.