Gallery demo page background bug workaround
Gallery demo page background bug workaround

Set gallery demo image scaleMode to `fill` as a workaround for the not
working setting of page background on the Android client.

Change-Id: I37dc948040e005e928047697f4d0e4ae702265cf

softnep0531/tabrisjs,softnep0531/tabrisjs,moham3d/tabris-js,eclipsesource/tabris-js,pimaxdev/tabris,mkostikov/tabris-js,pimaxdev/tabris,eclipsesource/tabris-js,mkostikov/tabris-js,eclipsesource/tabris-js,moham3d/tabris-js