Consider increasing size of content images

[agilare]

All images (flyers, etc.) uploaded for events are resized proportionally to a width of 600px

Consider extending this limit to 1200px in order to improve quality displayed especially in hi-res screens.

Maybe preserve also the version of 600px as an intermediate size for less demanding configurations (bandwidth, screen)

Warning : this improvement will increase the weight of images stored and it's difficult to match with current system where events that are repeated have also their images duplicated