Fixed issue #8159: (quexml-pdf) labels missing in text/number matrix questions

DEV: should be reviewed and cleared by Adam Zammit to
DEV: maintain consistency with quexml library

DEV: Adam, implemented an additional parameter "responsegrouplabel"
DEV: as I was unsure if using the existing parenttext would break
something
DEV: outside Limesurvey
Merge pull request #125 from mfaber/quexf_tnmatrixlabel205

Fixed issue #8159: (quexml-pdf) labels missing in text/number matrix questions