Add annotated slice dropdown

[cleaaum]

This PR adds a dropdown with the currently annotated slices. When a slice has annotations on it, this dropdown gets populated so the user can easily find which slices were annotated.

Implementation notes:

• When a user selects a slice to jump to, the dropdown value clears after it has been selected. This is to avoid confusion when a user goes to a different slice, there is no mismatch between the current slice and the slice in the dropdown.
• This dropdown gets updated every time an annotation is drawn, when a class is deleted, when all annotations are deleted on a slice (and when a specific annotation is deleted via the eraser).
• May need to rework/rephrase the UI

Closes #122

[github-actions[bot]]

Staging application has been deployed and is available at: https://dash5-services.plotly.host/ml-exchange-staging Production app name: ml-exchange Current branch name: addAnnotatedSliceDropdown Commit: bbb2e1e7b8c44100efeef63648873545887410a5

[cleaaum]

I've addressed all the comments!

• new notification added
• tooltip added
• label capitalization fixed
• prevent update added when selecting current slice

I've also refactored the notifications a bit. I created a function that generates a notification, you just pass the title, color and icon. I've also realized half the notification items are stored in a constants dict so I added all of the messages and icons to that dict for consistency.

[hannahker]

@cleaaum LGTM! 💃