Photoviewer: Allow using the Android back button to go back.
Photoviewer: Allow using the Android back button to go back.

Don't show back button on Android, as the system back button can
now be used.

Task-number: QTBUG-38122
Change-Id: Ia3a677f4626eaf34e23dfcc7997e4b850d8b7020
Reviewed-by: Alessandro Portale <c4179e69990f13917ee3505a5fdf6c5eb1b74ff4@digia.com>

mgrunditz/qtdeclarative-2d,qmlc/qtdeclarative,qmlc/qtdeclarative,mgrunditz/qtdeclarative-2d,qmlc/qtdeclarative,mgrunditz/qtdeclarative-2d,qmlc/qtdeclarative,qmlc/qtdeclarative,qmlc/qtdeclarative,mgrunditz/qtdeclarative-2d,qmlc/qtdeclarative,mgrunditz/qtdeclarative-2d,mgrunditz/qtdeclarative-2d,qmlc/qtdeclarative,mgrunditz/qtdeclarative-2d