Allow download methods configuration in gerrit.config. It was
included a section [download] in gerrit.config file to set the
scheme to be used in downloads.
This configuration hide or show ssh/http/anonymous git/anonymous
http and repo download tabs in change screen.
Bug: issue 583
Change-Id: I157135c6793771fc7b9e22bef5bae1a7d3b1da35
3f63044c4e