Added chat history to a room that is displayed on join.

With this update a new chat history definition is added on a per
room bases which allows operators to specify the number of chat
messages to store and present to the user on join.  Please see
the sample ini for room definitions.

common/pb/serverinfo_chat_message.proto

@@ -0,0 +1,16 @@
+syntax = "proto2";
+/*
+ * Chat communication of a user to a target.
+ * Targets can be users or rooms.
+ * These communications are also stored in the DB log table.
+ */
+message ServerInfo_ChatMessage {
+    optional string time = 1; // time chat was sent
+    optional string sender_id = 2; // id of sender
+    optional string sender_name = 3; // name of sender
+    optional string sender_ip = 4; // ip of sender
+    optional string message = 5;  // message
+    optional string target_type = 6; // target type (room,game,chat)
+    optional string target_id = 7; // id of target
+    optional string target_name = 8; // name of target
+}