Fix using context of Projects::UpdateContext (in admin section error, in public section - to next step if moving controlers)

Remove relative_url_root from path. Fixes #2602

Improve network graph

Revise projects/new text

Update Markdown example to use username

Update the Markdown example in the Help pages to use username instead of user.

The previous text implied projects can only be private. Projects can now be private or public.

Files and Commits render a 404 when running with relative_url_root.