Added WebDAV support for the working copies in the build agent
1. there's a WorkingCopyServlet in the build agent that will handle all url pattern: /workingcopy/*
e.g. In order to view the working copy of a project with id 1, the url will be "http://host/workingcopy/[projectId]"
2. support for read only access to working copies
3. can use Sardine as the WebDAV client
4. no security implementation yet.
#4 still needs to be discuss in the dev list. We currently don't have a database in the build agent so we can't use redback for the role-based authorization.