Fix Drawing shape

[mino-alpha]

Hello
I made some read/write fixes and additions to drawing

1. Allowed duplicate grouping
2. Made it possible to place multiple connectors in a group
3. Enabled reading and writing of Bezier curves

please merge if you like
by google translate

[tonyqus]

This change may break drawing.xml. Do you have any unit test or sample that I can take a look to make sure your code is really working.

[mino-alpha]

I am here.
2.sample.xlsx
1 sample.xlsx

[mino-alpha]

slightly more complicated example
3.sample.xlsx

[mino-alpha]

The test just read and write as below

		IWorkbook oWB = WorkbookFactory.Create( "sample.xlsx" );

		var fs = new FileStream( "sample-w.xlsx", FileMode.Create );
		oWB.Write( fs, true );
		oWB.Close();
		fs.Close();

[mino-alpha]

I added the shape's properties ID,Name

[tonyqus]

Is this PR still in progress? I see a few changes during the past days. If so, please put WIP prefix in the title.

[mino-alpha]

This concludes the functionality I want to add. thank you

[mino-alpha]

In my environment (fork branch) I don't get such test errors. . . . What should I do?

[tonyqus]

LGTM