Add refresh token api

lib/src/main/java/com/tuti/api/TutiApiClient.java

@@ -94,6 +94,17 @@ public void SignIn(SignInRequest credentials, ResponseCallable<SignInResponse> o
         sendRequest(RequestMethods.POST, serverURL + Operations.SIGN_IN, credentials, SignInResponse.class, TutiResponse.class, onResponse, onError, null);
     }
 
+    /**
+     * RefreshToken used to refresh an existing token to keep user's session valid.
+     * @param credentials
+     * @param onResponse
+     * @param onError
+     */
+    public void RefreshToken(SignInRequest credentials, ResponseCallable<SignInResponse> onResponse, ErrorCallable<TutiResponse> onError) {
+        sendRequest(RequestMethods.POST, serverURL + Operations.REFRESH_TOKEN, credentials, SignInResponse.class, TutiResponse.class, onResponse, onError, null);
+    }
+
+
     public void Signup(SignUpRequest signUpRequest, ResponseCallable<SignUpResponse> onResponse, ErrorCallable<TutiResponse> onError) {
         sendRequest(RequestMethods.POST, serverURL + Operations.SIGN_UP, signUpRequest, SignUpResponse.class, TutiResponse.class, onResponse, onError, null);
     }

lib/src/main/java/com/tuti/api/authentication/SignInRequest.java

@@ -1,9 +1,22 @@
 package com.tuti.api.authentication;
 
+import com.google.gson.annotations.SerializedName;
+
 public class SignInRequest {
     private String username;
     private String password;
 
+    public String getOldToken() {
+        return oldToken;
+    }
+
+    public void setOldToken(String oldToken) {
+        this.oldToken = oldToken;
+    }
+
+    @SerializedName("authorization")
+    private String oldToken;
+
     public String getUsername() {
         return username;
     }

lib/src/main/java/com/tuti/api/data/TutiResponse.java

@@ -11,6 +11,17 @@ public class TutiResponse {
     private String message;
     private String code;
 
+    public String getAuthorization() {
+        return authorization;
+    }
+
+    public void setAuthorization(String authorization) {
+        this.authorization = authorization;
+    }
+
+    private String authorization;
+
+
     public String getStatus() {
         return status;
     }