Check for update (#830)

- Closes https://github.com/inventree/inventree-app/issues/730

lib/settings/about.dart

@@ -1,5 +1,6 @@
 import "package:inventree/api.dart";
 import "package:inventree/app_colors.dart";
+import "package:inventree/inventree/update_check.dart";
 import "package:inventree/settings/release.dart";
 
 import "package:flutter/material.dart";
@@ -209,9 +210,24 @@ class InvenTreeAboutWidget extends StatelessWidget {
         title: Text(L10().version),
         subtitle: Text("${info.version} - Build ${info.buildNumber}"),
         leading: Icon(TablerIcons.info_circle),
+        trailing: UpdateChecker().newVersionAvailable
+            ? Icon(TablerIcons.alert_circle, color: COLOR_WARNING)
+            : Icon(TablerIcons.circle_check, color: COLOR_SUCCESS),
       ),
     );
 
+    UpdateChecker().checkForUpdate();
+
+    if (!UpdateChecker().newVersionAvailable) {
+      tiles.add(
+        ListTile(
+          title: Text(L10().versionNewer),
+          leading: Icon(TablerIcons.alert_circle, color: COLOR_WARNING),
+          trailing: LargeText(UpdateChecker().latestVersion),
+        ),
+      );
+    }
+
     tiles.add(
       ListTile(
         title: Text(L10().releaseNotes),