viewer: keep gain and exposure sensitive when auto is on.
viewer: keep gain and exposure sensitive when auto is on.

It allows to automatically return to manual setting when clicking on the
exposure and gain spin_buttons and sliders.

AravisProject/aravis,AravisProject/aravis,lu-zero/aravis,lu-zero/aravis,lu-zero/aravis,AnilRamachandran/aravis,AnilRamachandran/aravis,lu-zero/aravis,AnilRamachandran/aravis,AravisProject/aravis,AnilRamachandran/aravis,lu-zero/aravis,AravisProject/aravis,AravisProject/aravis,AnilRamachandran/aravis