Get better gallery boudaries

When there is not enough photo to have a scroll we should not have
boundaries in the middle of the screen.

Signed-off-by: Sébastien MICHEL <michoux@gmail.com>
Prevent open PhotoCaptionView on a previous photo

If you open a photo with photocaption view and bring it to background
(home key). If you ask to open another photo photoCaption View resumed
with the previous image. To prevent this we finish the activity on it go
onPause.

Signed-off-by: Sébastien MICHEL <michoux@gmail.com>