Add suppoort for list-style access to cells on row
Add suppoort for list-style access to cells on row

Individual cells on a row can be accessed list-style:
    row[0] returns the Cell for the Column where .index is 0.
    row[3] returns the Cell for the Column where .index is 3.
This *should* work even if you have fetched just a subset of the
columns of the sheet.

smartsheet-platform/smartsheet-python-sdk,smartsheet-platform/smartsheet-python-sdk