Ffmpeg versioning issues (#68)

* FFMPEG version cleanup

* Make sure attempts don't go on forever

* Use latest version when version not defined. Add latest to UI

src/api/serverproxy_manager.py

@@ -26,7 +26,7 @@ class ServerProxyManager:
     @classmethod
     def get_proxy_for_hostname(cls, hostname):
         found_proxy = cls.server_proxys.get(hostname)
-        if not found_proxy:
+        if hostname and not found_proxy:
             new_proxy = RenderServerProxy(hostname)
             new_proxy.start_background_update()
             cls.server_proxys[hostname] = new_proxy