feat(misc): a bunch of crude UI/UX tweaks

- display add time for later use
- basic keyboard navigation support
- remember last-used server address
- show connection error when attempt to connect to server

ConnectServerPage.qml

@@ -1,3 +1,4 @@
+import QtCore
 import QtQuick
 import QtQuick.Controls
 import QtQuick.Layouts
@@ -21,17 +22,19 @@ Control {
         TextField {
             id: baseUrlEdit
             Layout.fillWidth: true
+            placeholderText: "e.g. http://192.168.123.123:8080"
+            inputMethodHints: Qt.ImhNoAutoUppercase | Qt.ImhUrlCharactersOnly
             enabled: AppController.connectionState === AppController.NotConnected
         }
-        Item {
-            Layout.fillHeight: true
-            Layout.verticalStretchFactor: 1
+        Label {
+            text: AppController.lastErrorMessage
         }
         Button {
             Layout.fillWidth: true
             text: AppController.connectionState === AppController.NotConnected ? "Connect" : "Connecting"
             enabled: baseUrlEdit.enabled
             onClicked: function() {
+                settings.setValue("server_url", baseUrlEdit.text)
                 AppController.connectServer(baseUrlEdit.text)
             }
         }
@@ -40,4 +43,14 @@ Control {
             Layout.verticalStretchFactor: 3
         }
     }
+
+    Settings {
+        id: settings
+        Component.onCompleted: function() {
+            let srvUrl = settings.value("server_url", "")
+            if (srvUrl !== "") {
+                baseUrlEdit.text = srvUrl
+            }
+        }
+    }
 }