Add connection status indicator

gui/ui/state.slint

@@ -4,6 +4,12 @@ export struct SItem {
     amount: int,
 }
 
+export enum ConnectionStatus {
+    Idle,
+    Syncing,
+    Error,
+}
+
 export global State {
     in-out property <[SItem]> list: [
         { name: "Test 1", checked: true },
@@ -21,4 +27,5 @@ export global State {
     set-server-address(address) => {
         server-address = address;
     }
+    in-out property <ConnectionStatus> connection-status: ConnectionStatus.Syncing;
 }