Fix deprecation warnings

Replace trUtf8() by tr() and implement QAbstractItemModel::roleNames(),
fixing:

multimedia.cpp:76:5: note: in expansion of macro ‘Q_OBJECT’
multimedia.cpp:143:77: warning: ‘static QString QMultimediaDeclarativeModule::trUtf8(const char*, const char*, int)’ is deprecated [-Wdeprecated-declarations]
                 from multimedia.cpp:40:
....
qdeclarativecamerafocus.cpp:403:23: warning: ‘void QAbstractItemModel::setRoleNames(const QHash<int, QByteArray>&)’ is deprecated [-Wdeprecated-declarations]
     setRoleNames(roles);

Change-Id: I2648551a1b2774c45101ab1cad9e0ea3ab79ccbc
Reviewed-by: VaL Doroshchuk <valentyn.doroshchuk@qt.io>
Reviewed-by: Samuel Gaist <samuel.gaist@idiap.ch>