New git location

The work is done and you can find web browser views here:


https://gitbox.apache.org/repos/asf?p=cayenne.git

https://gitbox.apache.org/repos/asf?p=cayenne-modeler.git

https://gitbox.apache.org/repos/asf?p=cayenne-website.git


You can also commit directly to github: https://github.com/apache/cayenne


To make this work, all committers should first ensure they have 2FA 
enabled at github and then go here:

https://gitbox.apache.org/setup/


I've just tested the whole fork/pull request/merge process and it seems 
to work well. https://github.com/apache/cayenne-website/pull/2


Ari