link-device: apply new design and add QR code

src/app/constant/JamiStrings.qml

src/app/constant/JamiTheme.qml

src/app/qrimageprovider.h

src/app/settingsview/components/LinkDeviceDialog.qml

src/app/settingsview/components/LinkedDevicesPage.qml

src/app/settingsview/components/ManageAccountPage.qml

src/app/utils.cpp

src/app/utils.h