OpenXML: Hidden cells shouldn't be translated by default

[Chase Tingley]

The default behavior of the filter is to exclude hidden text, with an option to translate it. However, for XLSX we translate hidden cells by default and have no option.

We should align the default behavior with the rest of the filter by excluding hidden cells by default, and add an option to support their translation.

Cells can be excluded either by hiding a row or hiding a column. Both of these are handled in the worksheet markup. For columns, it's defined in a column header:

  <cols>
    <col min="1" max="1" width="21.1640625" customWidth="1"/>
    <col min="2" max="2" width="36.83203125" hidden="1" customWidth="1"/>
  </cols>

For rows, they're on the row data themselves:

    <row r="2" spans="1:2" hidden="1">

[Chase Tingley]

Fix issue #502 - OpenXML filter will ignore hidden XLSX cells by default

This also adds an option to expose them.  This option is called
"Translate Hidden Rows and Columns" in Rainbow.

→ <<cset 8cf6f453dbdc>>

[Chase Tingley]

The commit makes the following changes:

• By default, hidden rows and columns are no longer exposed for translation.
• A new option called "Translate Hidden Rows and Columns" is added to Rainbow to enable translation of this content.