Volunteers were not finding the button on the drop off side, so we're going to
try it over here.
Also, the backend implementation was mirroring the UI too much. We were passing
in a task to copy to along with the event. But we're also checking that the
event has exactly two tasks—a pickup and a drop off—and the copying only goes
one way so the extra param was not needed.
This refactors the TaskLogReplacer so that all you need to pass is the event in
question.
Also, because the button is not "push" instead of "pull" it's difficult to know
if anything actually happened. The button now changes from "Copy logs to drop
off task" to "Copied" when clicked and changes back if the page is reloaded or
someone creates a new task log.