Make Header Logo configurable

[belfhi]

Make Header Logo configurable

Summary

At DESY The default Logo is blue and while that is file for the /login page, the logo which is also displayed on the header is not (or barely) visible. If would be nice to be able to use a different logo file which has a more appropriate colour scheme.

Steps to Reproduce

mount a blue site-logo.png file to /usr/share/nginx/html/assets/images/

Current Behaviour

Ses that the logo is not visible in the header. No config option available to change this (?)

Expected Behaviour

A different logo should be used that was more visible, for example DESY PR has a white version of our logo available that would work very well.