Add config vars $wgChatKicks & $wgChatSocialAvatars

$wgChatKicks, disabled by default, allows the 'kicking' of users from chat
$wgChatSocialAvatars, enabled by default, whether to give users avatars
from SocialProfile
Plus some reorganisation

Change-Id: I391ad14b7b98d091b929d5d1b27e6ae43ecebbb4