Add support for Shapes API Completed

Many of our Spreasheets are used as aids to entering data into down-stream systems, and include various SHAPES (ovals, rectangles, lines)...

I do not see any way to convert existing (unsupported) shapes into SUPPORTED shapes (I believe the Shapes API is limited to GemBox.Document).

I suppose, it might be possible to SAVE a spreadsheet in a format that could be ingested by GemBox.Document, and then iterate through the "unsupported" shapes in the Spreasheet, adding them to the Document - but I would argue that: A) Gembox.Spreadsheet (and Document, for that matter) should support ALL of the Shapes (including "obsolete" shape objects/groups); B) Shapes API should be supported in GemBox.Spreadsheet.