Mostly code in AdCanvas, IPanel and LoadingPanel to understand what
AApplet is doing.

These were helpful in tracking down the layout shift bug fixed in
LobbyPanel in the next commit.

Resizing the applet caused the lobby screen to do a new layout and
since it was using the default LayoutManager (FlowLayout), the panels
were being placed in unintended places. Most other classes explicitly
set the layout manager to null to avoid this, however, looks like this
was overlooked in LobbyPanel.

Previously, this tried to open a new page in the browser, however,
in our environment, appletContext was null and was throwing an
exception.

This was fixed by destroying the game applet and reinitializing it when
the retry button is clicked.

Reinitalizing the applet caused its size to get re-measured which was
leading to layout bugs after retries, this was fixed by hardcoding the
applet width and height in AApplet. Since the whole game is hardcoded
for this size, this does not result in any problems elsewhere.

This revealed artificial delays in joining lobbies, probably as a means
of flood protection. This can be verified by going into a single player
lobby and clicking "Multiplayer", then "Single player" again rapidly and
seeing a blank screen stuck on the sleep timer.

Previously the delay was a ladder of 3 -> 7 -> 15 seconds and switching
between lobbies was annoying. Now it's faster and the change does not
seem to cause any issues. I still opted to keep a one second delay in
case removing the delay would break something.