added: TimeZone struct (core)

this class has information about a time zone (utf offset, daylight saving time)
       and methods for converting between UTC and local time
       structs User and Config has a TimeZone object
       System::ToLocal() and System::ToUTC() uses it for converting
       (depending whether a user is logged or not)


git-svn-id: svn://ttmath.org/publicrep/winix/trunk@842 e52654a7-88a9-db11-a3e9-0013d4bc506e

core/users.h

@@ -38,7 +38,6 @@ public:
 
 	void Clear();
 	void ReadUsers(Db * db);
-	void SetTimeZoneOffset(int offset); // !! temporarily one time_zone for all users
 	bool AddUser(const User & user);
 	bool IsUser(const std::wstring & name);
 	User * GetUser(long user_id);