ServerConnectionDialog: Keep selected entry at fix position

[Krzmbrzl]

As of the current status of the main branch, the server connection dialog seems to continuously populate the server-list once the card for a particular region is being expanded. This leads to further entries being added to the list while the user is browsing it.

Right now the user can select a server, wait a second or so and his/her selection is no longer visible as it scrolled out of the window. This makes it really confusing to use this list.

I think this could be improved by checking the current position of the selected entry once it has been clicked on and then force that entry to remain at that position while the other entries are being added to that list. This should be doable by adjusting the scroll of the list accordingly.