Improve styling of the photo stream

### I added some lines by forming the display of photos in a gallery.

ScreenShot :  
http://owncloud.s-pichard.fr/public.php?service=files&t=0b789c48e9b3f49b176e2c228594b6fc

* This is my first contribution and first use Git.
* I do not have a test server, so I have not been tested on a POD test. 
* These are just a few lines in CSS to improve the visibility of photos in the profile.
* I have not been able to test my code in real condition, but it has a good record with the Stylish extension.

Thank you