Update the Chinese conversion table for Chinese WikiProjects
The Chinese conversion table is substantially updated to fix a lot of
bugs reported in recent years, and the script generating conversion
table (LanguageZh.php) is also modified to facilitate the maintenance.
Zh-sg and zh-my is set to fallback to zh-cn to improve reading
experience, since there is only trivial difference among them, just like
zh-hk and zh-mo. Further optimization for zh-sg and zh-my will be
performed in local conversion table of Chinese WikiProjects.