Ensure all operations of PSE are cancelled

When launching a larger PSE, if the user wants to cancel it immediately, only the operations that were generated before this action will be canceled. The others continue running. In some cases, the status of the burst remains Pending instead of Canceled.

Suggestions to fix this:

1. We could make the Cancel button inactive until all the PSE operations are generated. When it becomes active again, all operations are generated and can be safely canceled. 
2. Before launching one operation, check the status of the PSE group that operation is part of. If the status is Cancelled, then do not start the current operation and put its status on Cancelled as well.

It might be necessary to use both options above.

Also, we should ensure that there is a rule for these statuses, e.g. once an operation has status ERROR/SUCCESS, it cannot be switched to CANCELLED.