Disable delete button during request to delete entity

[matthew-white]

Let's say I check "Delete immediately without confirmation until I leave the page" while deleting an entity from the entities table. If I then go on to delete another entity, nothing happens to the delete button when I click it. The button is not disabled, and no spinner is shown. I'm able to click the button again, sending a second request to delete the entity.

When we added submission deletion from the submissions table (getodk/central-frontend#1043), we set it up so that the delete button changes after it is clicked. The button is disabled, and a spinner is shown. This issue is to do something similar for entity deletion.