`Project` uses `ProjectPathValidator` which is now a
`NamespaceValidator` that skips the format validation.
That way we're sure we are using the same collection of reserved
paths.
I updated the path constraints to reflect the changes: We now allow
some values that are only used on a top level namespace as a name for
a nested group/project.
* add parent_id field to namespaces table to store relation with nested groups
* create routes table to keep information about full path of every group and project
* project/group lookup by full path from routes table
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
