Add ability to clear the proxy address.

Closes #12499

app/src/main/java/org/thoughtcrime/securesms/util/SignalProxyUtil.java

@@ -67,6 +67,11 @@ public final class SignalProxyUtil {
     startListeningToWebsocket();
   }
 
+  public static void disableAndClearProxy(){
+    disableProxy();
+    SignalStore.proxy().setProxy(null);
+  }
+
   /**
    * A blocking call that will wait until the websocket either successfully connects, or fails.
    * It is assumed that the app state is already configured how you would like it, e.g. you've