OpenXML Filter: XLSX: provide a specific option for text exclusion by color

Currenlty the exclusion is supported by configuration option for DOCX documents:

• net.sf.okapi.filters.openxml.ConditionalParameters#tsWordExcludedColors

This can be reflected in the following string configuration:

tsWordExcludedColors.i=1
yyy0=Red

So, it would be better to have another option for Excel.

Related issue #1433 (closed).