add option to ping servers imediately, ignoring waiting for serverupdateinterval

[nochinator]

Fixes #915

Changes proposed in this request:
serverbrowser.cpp:

• add argument "update_now" to functions updateservers and refreshservers. it defaults to 0
• updateservers only passes it to refreshservers
• updatefrommaster now calls refreshservers with update_now set to 1
• in refreshservers the check for if enough time has elapsed based on serverupdateinterval now has an OR check to see if update_now is 1, if it is then it will update regardless of when the last update was

online.cfg:

• when gameui_online_update is called it checks to see if we have pinged before in this session, if we have then call updateservers with update_now at the default value (0), if not then call it with update_now set to 1 forcing an immediate ping regardless of when the last ping was

With these changes the server list will ping servers immediately upon being opened (before the animation) making the only delay in the time it takes to ping