Add possibility to define supported localizations for online installer (Updates.xml file name)

Now the online client tries to find localized Updates.xml file from server
causing server side logs to get full of "file not found" warnings.

Add possibility to define supported localizations in config.xml
or add possibility to force the client to use default file "Updates.xml".

The server side logs are literally full of these warning messages which makes it difficult to see other issues there.