MOD: `MJRefreshBackStateFooter`添加获取指定状态下title的方法

MJRefresh/Custom/Footer/Back/MJRefreshBackStateFooter.h

@@ -13,4 +13,7 @@
 @property (weak, nonatomic, readonly) UILabel *stateLabel;
 /** 设置state状态下的文字 */
 - (void)setTitle:(NSString *)title forState:(MJRefreshState)state;
+
+/** 获取state状态下的title */
+- (NSString *)titleForState:(MJRefreshState)state;
 @end

MJRefresh/Custom/Footer/Back/MJRefreshBackStateFooter.m

@@ -43,6 +43,10 @@ - (void)setTitle:(NSString *)title forState:(MJRefreshState)state
     self.stateLabel.text = self.stateTitles[@(self.state)];
 }
 
+- (NSString *)titleForState:(MJRefreshState)state {
+  return self.stateTitles[@(state)];
+}
+
 #pragma mark - 重写父类的方法
 - (void)prepare
 {