nsIFontPackageHandler Interface

 Set the font package handler for Gecko
 @param aFontPackID a font package ID.
 The id have the following naming convenation 
  name_space:name
 we currently define one name space
    lang - a font package for a particular language group
 and udnder the lang name space, we use the language code to identify
 the package, below are the defined packages
   ja - Japanese font package ("lang:ja")
   ko - Korean font package ("lang:ko")
   zh-TW - Traditional Chinese font package ("lang:zh-TW")
   zh-CN - Simplified Chinese font package ("lang:zh-CN")
 In the future, we may want to add
    ar - Arabic font packges ("lang:ar")
    he - Hebrew font packages ("lang:he")
    th - Thai font package ("lang:th")
 other name space are reserved for now.
 After the installation, the font package handler should call
 nsIFontPackageService::FontPackageHandled and pass back the aFontPackID
 
 This interface sould be implemented by the embedding application
 In the other hand the nsIFontPackageProxy is internal to Gecko