Revert "fix user average elo counter using mongodb aggregation"

This reverts commit 260b51be9087cce589c77e4d96caddd104460ac2.
Revert "use patched reactivemongo"

This reverts commit 2821b5973826aab3039c51d8a5f6f858b032ec74.
tweak timeline borders
fix message sending to predefined user on error
always show player counter left border
fix message form
show message icon instead of text in top menu
preview unread messages
improve message previews