暴露 LoadingView 给外部 (#1288)

MJRefresh/Custom/Header/MJRefreshNormalHeader.h

@@ -10,6 +10,9 @@
 
 @interface MJRefreshNormalHeader : MJRefreshStateHeader
 @property (weak, nonatomic, readonly) UIImageView *arrowView;
+@property (weak, nonatomic, readonly) UIActivityIndicatorView *loadingView;
+
+
 /** 菊花的样式 */
-@property (assign, nonatomic) UIActivityIndicatorViewStyle activityIndicatorViewStyle;
+@property (assign, nonatomic) UIActivityIndicatorViewStyle activityIndicatorViewStyle MJRefreshDeprecated("请使用 loadingView 进行设置");
 @end

MJRefresh/Custom/Header/MJRefreshNormalHeader.m

@@ -30,7 +30,7 @@ - (UIImageView *)arrowView
 - (UIActivityIndicatorView *)loadingView
 {
     if (!_loadingView) {
-        UIActivityIndicatorView *loadingView = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:self.activityIndicatorViewStyle];
+        UIActivityIndicatorView *loadingView = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:_activityIndicatorViewStyle];
         loadingView.hidesWhenStopped = YES;
         [self addSubview:_loadingView = loadingView];
     }
@@ -51,7 +51,7 @@ - (void)prepare
 {
     [super prepare];
     
-    self.activityIndicatorViewStyle = UIActivityIndicatorViewStyleGray;
+    _activityIndicatorViewStyle = UIActivityIndicatorViewStyleGray;
 }
 
 - (void)placeSubviews