App Down Dialog

There is a dialog that will pop up any time the app opens (#317). The reason is because Port Authority servers have been down consistently for the past 4 weeks. This is a temporary solution to the problems since I have no control over:

1. When the server comes back up
2. If the server is truly up or down

Details are here: https://github.com/rectangle-dbmi/Realtime-Port-Authority/wiki/Port-Authority-Server-Downtimes

Otherwise, there are no other code changes to this release.