Add basic conditional formatting writer support.
Add dataBar and colorScale write support
Add new private class XlsxColor
Make use of XlsxColor for ConditionalFormatting
Don't lost conditionalformatting data when edit an existing file
Remove qDebug statement
Format refactor: Don't store default properties

So that fontKey/fillKey/borderKey/formatKey will be unique for the same
formats
XlsxColor refactor