Multiviewport - example crashes on exit

Example crashes in global destructor when destroying QVector<QString>. Issue comes from plugins having constant string data.

This bug report is for Qt3D to avoid/workaround the issue described in QTBUG-49061.

crash stack

1 QVector<QString>::~QVector()   0x1000d3c03    
2 __cxa_finalize_ranges          0x7fff8f9bf46b 
3 exit                           0x7fff8f9bf76f 
4 start                          0x7fff8ea495b4