New connect api

Includes some fixes/enhancements:

-  SLP selection dialog: make OK button default, display the default SCC URL
- Do not set repository status (enabled/autorefresh) for service repositories, libzypp has been fixed to set correctly the status from the service (libzypp >= 14.21.0)
- Fixed credentials file removal (File.unlink is correct)
- Do not use long and short extension name together
why this change? Reason for this was to cache finding addons here. This way you need to call again listing of available addons. Idea behind is that cache should live together with class that it cache as usually such class know the best when to invalidate it.