Intercept modal dismissal with unsaved changes

[aswallace]

Addresses two small requests for the editing modal:

• Removes redundant tooltips from buttons
• Adds a warning pop-up if user dismisses the modal after they've already entered annotation data
  • Warning logic needs to be global to the whole edit modal instead of just the form component because dismissing can mean clicking cancel, clicking the 'x' or just clicking outside of the modal
  • The pop-up currently only appears for the 'New annotation' pathway after a user enters data for the new ann. and clicks next (per discussion, anything before that is easy to re-enter so warning is not needed)
  • Uses show/hide with css instead of js conditionals since we need the rendered data to persist

closes #344