Replaced CPlayerInterface::pim with CGuiHandler::interfaceLock

- Removed CPlayerInterface::pim since this lock does not actually
protects LOCPLINT but rather entire game UI state
- added more logical CGuiHandler::interfaceLock
- interface lock is now non-recursive and is locked only once by initial
caller that want to access GUI

client/mainmenu/CMainMenu.cpp

@@ -304,8 +304,6 @@ CMainMenu::CMainMenu()
 
 CMainMenu::~CMainMenu()
 {
-	boost::unique_lock<boost::recursive_mutex> lock(*CPlayerInterface::pim);
-
 	if(GH.curInt == this)
 		GH.curInt = nullptr;
 }