Only call the config server when needed

[noemifrisina]

The config server has been correctly set up so that it can get the value for the crosshair X,Y from the display.configuration file. However testing on the beamline has shown that instead of only poking the config server as-needed (on opening the screen, on changing the zoom level, on moves) it continuously pokes it. This is a bit overkill and it makes it very difficult to read the logs and debug other issues.