增加删除按钮，长按时进入编辑状态。
#	new file:   DragGridView/res/drawable-hdpi/add_more.png
#	renamed:    DragGridView/res/drawable-hdpi/com_tencent_open_notice_msg_icon_big.png -> DragGridView/res/drawable-hdpi/com_tencent_big.png
#	new file:   DragGridView/res/drawable-hdpi/delete_disabled.png
#	new file:   DragGridView/res/drawable-hdpi/delete_normal.png
#	new file:   DragGridView/res/drawable-hdpi/delete_pressed.png
#	new file:   DragGridView/res/drawable-hdpi/music.png
#	new file:   DragGridView/res/drawable/btn_delete_selector.xml
#	modified:   DragGridView/res/layout/grid_item.xml
#	modified:   DragGridView/src/com/example/draggridview/DragAdapter.java
#	modified:   DragGridView/src/com/example/draggridview/DragGridView.java
#	modified:   DragGridView/src/com/example/draggridview/DragGridViewActivity.java