Feature request: automatically set sheet size to content size

[daniilS]

Currently the default height and width of the MainTable is determined by the default canvas size. This means that when putting a Sheet with only a few rows/columns inside an application, it will fill it up with a lot of empty space. It would be nice if there was an option to make the sheet only request the size it needs to fit its content, i.e. automatically update MainTable.configure(height=) to self.row_positions[-1] + 1 + self.empty_vertical and the same for its width, whenever the content is updated.