font size in config, and two bugs with private chat squashed

bigbluebutton-client/locale/en_US/bbbResources.properties

bigbluebutton-client/resources/config.xml.template

...t/src/org/bigbluebutton/modules/chat/model/ChatOptions.as

...c/org/bigbluebutton/modules/chat/views/AddChatTabBox.mxml

...ent/src/org/bigbluebutton/modules/chat/views/ChatBox.mxml

...nt/src/org/bigbluebutton/modules/chat/views/ChatView.mxml