Delete annotation from anno list

[mejackreed]

Split out from #6

Delete annotation

• Tooltip: Delete
• Icon: delete_forever - https://material.io/resources/icons/?search=trash&icon=delete_forever&style=sharp

If the user selects the Delete action:

• Update the sidebar annotation item and canvas target highlighting
• Display a Dialog component (I think we want an "alert" style, in that it should be pretty simple.)

Dialog details:

• Text: Delete this annotation?
• Buttons: CANCEL and DELETE

If the user selects the Cancel button, the dialog disappears and we remove the current annotation item highlighting.

If the user selects the DELETE button:

• Remove the annotation from the annotationpage
• Update the annotation sidebar to reflect the deleted annotation's removal and update the new annotation count message
• Display a snackbar component with a confirmation message:

Snackbar details:

• Position: top-center
• Background color: primary_color
• Text: Annotation saved
• Button: DISMISS
• Auto-dismiss: after 3 seconds