Bring HearthStats window to the front for important events

Some people weren't noticing important popups like the "enter your user key" or "match result not detected" because the HearthStats window was in the background. Now we attempt to bring the window to the front whenever an important popups occurs so that you don't miss the popup.
Added exception handler for OS X notifications setting

Just in case it causes problems on Windows machines, it's safer to catch and ignore exceptions accessing it.