Fix word-count logic in protected segments

[YvesS]

Currently the segment the XLIFF filter plugin set as protected (state='final' and translate='no'), have no specific handling of the word count.

But they very likely should, as the ProtectedPart object has various method that seem to be providing info about this.

[YvesS]

Added HTML to the filters. This resolves issue #4.

→ <<cset b487580a7bf9>>