Add confirmation modals and loading spinners for certain actions

[kevinaboos]

Loading spinners needed

• Next to the "Save Name" / "Cancel" buttons in the AccountSettings widget Add loading spinners to Account Settings buttons #710
• Next to the "Upload Avatar" / "Delete Avatar" buttons in the AccountSettings widget Add loading spinners to Account Settings buttons #710

Confirmation modals needed

• A positive confirmation modal for the "Direct Message" button in the UserProfileSlidingPane Show a confirmation modal before auto-creating a new DM room #734
  • This should only be shown before we create a new direct message room. If one already exists, we can safely jump to it.
• A new top-level negative confirmation modal for deleting or removing anything. This should be used for: Add a unified, top-level confirmation modal for delete/remove actions #723
  • Deleting your avatar Add a unified, top-level confirmation modal for delete/remove actions #723
  • Re-use the same negative confirmation modal for deleting (redacting) a message. Add a unified, top-level confirmation modal for delete/remove actions #723
  • Removing a TSP wallet entry. Add a unified, top-level confirmation modal for delete/remove actions #723

Other

• A change to the NavigateToRoom action that specifies whether we're the room has already been joined and we're waiting for it to be loaded (e.g., after creating a DM with a user), or if we actually do want to display the join room modal.
  • This is necessary because it doesn't make sense to prompt the user to join a room that they just created.
  • In the former case, the modal should just be a simple "loading room" modal that just displays a basic message about waiting to load the room, a simple loading spinner, and a gray cancel button that allows the user to clear the modal if it's taking too long to load that room.