GNUstep web install option to use latest releases instead of master branch

[mcarans]

It would be great to be able to pass a parameter to run the script so that instead of using the latest master, the current released version of each library is used instead (eg. libobjc 2.3, gnustep base 1.31.1 as of now).

Also it would be great to have an option to only build what's required for gnustep base if gnustep gui isn't needed.