Rewrite the count up/down logic to deal with null matches.

Previously, it assumed that the nextMatch existed all the time. I'm
not really sure why this wasn't an issue a the SR2014 competition,
but it does cause issues locally when testing around the final.
Remove that assumption so that we don't get null errors in the final.

Change-Id: I5842e39f36181c462a856626f71254b8501eb2f1
Ensure that the final starts properly.

Because there's no next match, we need to trigger the countdownView's
update a bit manually. Doing so hides it allowing the match to begin.

Change-Id: I4795472c498e0a8217f57d8d6bdd8f6117da4377
Clear the screens when there's nothing to show

This is mainly an issue after the final, where there is no next
match nor a current match. In such cases we just clear the screens
for lack of anything better to display.

Change-Id: I0ba38c52ba5948cb030b7699b099d88a949d5af7