feat: add missing Sign Up and Sign In items fields in Application (#87)

* fix: Application Sign Up and Sign In fields for organisation (#86)

The Application entity found at org.casbin.casdoor.entity.Application is missing required fields that are needed to correctly load the OAuth2 page and admin dashboard.

Fields missing are:

- Sign Up Items
- Sign In Items
- Sign In Methods

Due to these missing fields the database is holding null. This results with a front-end error as the UI is expecting an array (even if it's an empty array) in comparison to null for both the OAuth2 login page, and the Admin Dashboard.

* Update Application.java

---------

Co-authored-by: Yang Luo <hsluoyz@qq.com>

src/main/java/org/casbin/casdoor/entity/Application.java

@@ -57,6 +57,9 @@ public class Application implements Serializable {
     public int formOffset;
     public String formSideHtml;
     public String formBackgroundUrl;
+    public List<SigninMethod> signinMethods;
+    public List<SigninItem> signinItems;
+    public List<SignupItem> signupItems;
 
     public Application() {
     }
@@ -71,4 +74,30 @@ public Application(String owner, String name, String createdTime, String display
         this.description = description;
         this.organization = organization;
     }
-}
+
+    public static class SigninMethod {
+        public String name;
+        public String displayName;
+        public String rule;
+    }
+
+    public static class SigninItem {
+        public String name;
+        public boolean visible;
+        public String label;
+        public String placeholder;
+        public String rule;
+        public boolean isCustom;
+    }
+
+    public static class SignupItem {
+        public String label;
+        public String name;
+        public String placeholder;
+        public boolean prompted;
+        public String regex;
+        public boolean required;
+        public String rule;
+        public boolean visible;
+    }
+}