Enable to user to stop a de-identification request

[tschaffter]

Is your proposal related to a problem?

Maybe the request takes too long. The user should be able to stop the request to get back control of the app, e.g. changing settings that may have an impact on the runtime.

Describe the solution you'd like

Replace the button "De-identify Note" by a button "Stop de-identification" while the de-identification is running.