Minor fix

* Fix selection error when use delete after to delete the last tas unit
* Fix sel_rect display error
* Add some documents
* Fix layout becoming confusing when secondly open file.

BallanceTASEditor/Language/CHS.xaml

@@ -31,6 +31,7 @@
     <sys:String x:Key="ui_MainWindow_StatusBar_Mode_Cursor">选择模式</sys:String>
     <sys:String x:Key="ui_MainWindow_StatusBar_Mode_Fill">填充模式</sys:String>
     <sys:String x:Key="ui_MainWindow_StatusBar_Mode_Overwritten">画笔模式</sys:String>
+    <sys:String x:Key="ui_MainWindow_StatusBar_OverwrittenPaste">覆盖式粘贴</sys:String>
     <sys:String x:Key="ui_MainWindow_StatusBar_Selected">已选择：</sys:String>