Simple addin that demonstrate the bug in Excel add-in (Office 365)

Steps to load the addin:

1. Share the root folder of this project and Add as trusted catalog (or copy the mainfest existing catalog)
2. Start the server: python -m http.server 8080
3. load the add-in in excel

About the bug: If there is a single interval related pane - closing it will stop the interval. If there is another pane open when closing the pane with interval - it will continue to run until reopening the interval pane

Steps to reproduce the bug: there are 3 different scenarions: scenario A:

1. Open the "interval update pane"
2. Click the "Random interval!" button (see how values change rapidly in the active worksheet)
3. Close the "interval update pane" Result: Values stop changing rapidly

Senario B:

1. Open the "Highlight pane"
2. Open the "Interval update pane"
3. Click the "Random interval!" button (see how values change rapidly in the active worksheet) Mid-step-result: Values keep on changing rapidly
4. Close the "Interval update pane" Mid-step-result: Values keep on changing rapidly
5. Close the "Highlight pane" Mid-step-result: Values keep on changing rapidly
6. Open the "Highlight pane" Mid-step-result: Values keep on changing rapidly
7. Close the "Highlight pane" Mid-step-result: Values keep on changing rapidly
8. Open the "interval update pane" Result: Values stop changing rapidly

Scenario C:

1. Open the "Highlight pane"
2. Open the "Interval update pane"
3. Click the "Random interval!" button (see how values change rapidly in the active worksheet) Mid-step-result: Values keep on changing rapidly
4. Close the "Highlight pane" Mid-step-result: Values keep on changing rapidly
5. Open the "Interval update pane" Result: Values stop changing rapidly

To summarize that: If there is a single interval related pane - closing it will stop the interval. If there is another pane open when closing the pane with interval - it will continue to run until reopening the interval pane