Raise group avatar filesize limit to 200kb, fixes #8527
Created by: Razer6
With GitLab 7.6, the file size limit for user avatars was raised from 100kb to 200kb.
Since group avatars use the same view as user avatars there is now a conflict because UI says a limit of 200kb although the model validates against 100kb. This PR raises the file size limit for group avatars from 100kb to 200kb.