Cleanup max user check at login

This change accomplishes two goals.  The first is it moves the checking
for if the servers set user limit is reached out of the socket interface
and into the protocol handler portion of the code (were it should live).
It also eleminates the need for a DB query at login to check the user
count.  The user account is actually already maintained by the server
and a function already existed to get the user count total.

common/pb/response.proto

@@ -37,6 +37,7 @@ message Response {
         RespRegistrationAcceptedNeedsActivation = 33; // Server accepted cient registration, but it will need token activation
         RespClientIdRequired = 34; // Server requires client to generate and send its client id before allowing access
         RespClientUpdateRequired = 35; // Client is missing features that the server is requiring
+        RespServerFull = 36; // Server user limit reached
     }
     enum ResponseType {
         JOIN_ROOM = 1000;