Install kernel/Change Kernel doesn't work in the interactive window

[rchiodo]

Create a venv with no ipykernel

Send code to interactive window

Click change kernel

Dialog pops up a second time and you're not allowed to change a kernel.

[DonJayamanne]

This is blocked by #6135
I've added a work around that will disable changing of kernels.
Also we get a horrible UX, we get the modal dialog twice for Interactive (just again part of the current code flow, we didn't notice this earlier because they weren't modal dialogs).

[DonJayamanne]

I'm going to change this from a modal to non-modal for Interactive, as its a very poor UX. (reverting to the exiting UI, which results in two messageboxes, at least they are not modal)