update player list in lobby gracefully for better user experience
fixed child removal
fixed relayout on draw
refactored child remove/replace into ScrollPanelWidget
fixed scrolling on child remove
added moving average to contrails to smooth them when aircraft are circling
refactored Average method in PPos
Merge pull request #2798 from bidifx/contrail

smooth contrails
Merge pull request #2796 from Mailaender/attack-sync

Put attack traits into the syncreport.log
Merge pull request #2789 from bidifx/lobby

update player list in lobby gracefully for better user experience
add tab cycle key to setting GUI
fixes #2791 don't crash on powerdown hotkey when playing cnc
pull cnc sell/repair button hotkeys from settings
fixes #2785 don't crash when last player leaves game in cnc