Added translated key registeration.

Todo:
1. let translate function have a dictionary (sync with localStorage
through store.js, exportable);
2. let findRemainingI18nKey function export keys and related dom nodes
separately. (keys map can be extended so the final listing can be
obtained and compared with or used as dictionary);
3. find a way to obtain keys map(resource keys) from clicking the i18n
tab (to clip-board maybe if json file can not be exported);
4. find a way to load/restore translations per locale(through url)