SchemaProvider::getSelfSubUrl returns URl with and without ending '/' depending on input resource

[neomerx]

If resource is given it returns something like '/posts/2' (note no ending '/') but if null given it returns '/posts/' (with ending '/'). This lead to double slashes in URLs for resources without identities e.g. '/profile//relationships/comments'.

Need more consistency. It should be no trailing '/' in all cases.

[neomerx]

It will be a breaking change. Sub-url in Schema (if set) had to have both starting and ending slashes e.g. '/posts/'. Now it must have only starting.

As this feature is optional it won't affect majority of users. Though it must be documented.