support videochat-services not suppporting rooms

some videochat-services do not support adding random rooms to the url,
users let people in manually, so they can always use the same url.

as hacks as hiding the genrated random room behind `#$ROOM` or `?=foo=$ROOM`
does not always work, this pr introduces the parameter `$NOROOM` that is
just replaced by the empty string.

see https://support.delta.chat/t/videochat-with-webex/1412
for further details.

src/message.rs

@@ -695,6 +695,13 @@ impl Message {
         // add/replace room
         let url = if url.contains("$ROOM") {
             url.replace("$ROOM", &room)
+        } else if url.contains("$NOROOM") {
+            // there are some usecases where a separate room is not needed to use a service
+            // eg. if you let in people manually anyway, see discussion at
+            // https://support.delta.chat/t/videochat-with-webex/1412/4 .
+            // hacks as hiding the room behind `#` are not reliable, therefore,
+            // these services are supported by adding the string `$NOROOM` to the url.
+            url.replace("$NOROOM", "")
         } else {
             // if there nothing that would separate the room, add a slash as a separator;
             // this way, urls can be given as "https://meet.jit.si" as well as "https://meet.jit.si/"
@@ -2304,6 +2311,26 @@ mod tests {
         assert_eq!(instance, "basicwebrtc:https://basic.stuff/12345ab");
     }
 
+    #[async_std::test]
+    async fn test_create_webrtc_instance_noroom() {
+        // webrtc_instance may come from an input field of the ui, be pretty tolerant on input
+        let instance = Message::create_webrtc_instance("bla.foo$NOROOM", "123");
+        assert_eq!(instance, "https://bla.foo");
+
+        let instance = Message::create_webrtc_instance(" bla . foo $NOROOM ", "456");
+        assert_eq!(instance, "https://bla.foo");
+
+        let instance = Message::create_webrtc_instance(" $NOROOM bla . foo  ", "789");
+        assert_eq!(instance, "https://bla.foo");
+
+        let instance = Message::create_webrtc_instance(" bla.foo  / $NOROOM ? a = b ", "123");
+        assert_eq!(instance, "https://bla.foo/?a=b");
+
+        // $ROOM has a higher precedence
+        let instance = Message::create_webrtc_instance("bla.foo/?$NOROOM=$ROOM", "123");
+        assert_eq!(instance, "https://bla.foo/?$NOROOM=123");
+    }
+
     #[async_std::test]
     async fn test_get_width_height() {
         let t = test::TestContext::new().await;