to use cell span, there will need a MetaList class and meta function to provide span condition

• Merged cell definition should not overlap
• header is part of meta list, sort or delete row/column should update header defititon
• Rearrange column may not work
• Column id with "!" denote row span
• text value in span cell from top left cell

sample header format:
          
              {
                  "header" :  {
                   'row_number_from_0': {'column_id': number_of_column_span...},
                   '8': {'duration': 1, 'duration!': 8, 'a4': 2, 'a4!': 3}, // "duration!" is row span
                   },
                  "headerCss":{
                    '0': {'a1': "c1", "a5": "a5", "duration": "merged"}, //"css style block"
                   '4': {'a3': "merged"},
                   '8': {'duration': 'merged', 'a4': "merged"}, 
                  } 
                 };