使用进度条控制画布控件缩放

- 移除顶部放大/缩小按钮，改用底部SeekBar进度条控制
- 缩放范围0.1-5.0对应进度条0-100
- 添加setScaleFactor()方法

gallery/src/main/java/cc/winboll/studio/gallery/ZoomContainerView.java

@@ -13,7 +13,7 @@ import android.widget.FrameLayout;
 
 public class ZoomContainerView extends FrameLayout {
     private float scaleFactor = 1.0f;
-    private float minScale = 0.5f;
+    private float minScale = 0.1f;
     private float maxScale = 5.0f;
     private static final float ZOOM_STEP = 0.25f;
     
@@ -98,6 +98,12 @@ public class ZoomContainerView extends FrameLayout {
         return scaleFactor;
     }
     
+    public void setScaleFactor(float scale) {
+        scaleFactor = Math.max(minScale, Math.min(scale, maxScale));
+        requestLayout();
+        invalidate();
+    }
+    
     public void resetZoom() {
         scaleFactor = 1.0f;
         invalidate();