Remove more QByteArray<->QString conversions

Remove more QByteArray<->QString conversions

Prefer to store types as QStrings. It's only when we manipulate
raw (compiled, meta-)data that utf conversion is needed.

Change-Id: Ie138a69c9a409804e1b90b21c1d60dedea35bddb
Reviewed-on: http://codereview.qt-project.org/5781
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Roberto Raggi <roberto.raggi@nokia.com>