RFCs image viewer: make image viewer scaling better adapted to the screen size

[Fania Bremmer]

In the image viewer:

RFC1:
** Proposed Change **
Give the user the chance of seeing the picture always best fit to the 
screen height or width as a default.

** Reason For Change **
The pictures are currently scaled quite random. Some have the maximum 
height, other are somewhat smaller.

RFC2:
** Proposed Change **
The zooming interacts with the sliding to the next image - Thomas 
already wrote about this topic a while ago. This needs to be fixed.

** Reason For Change **
It happens a lot of time that users scale an image but then move on to 
the next image without intention. How can we make sure, that the zooming 
gesture and the swipe gesture are beeing distinguished properly?