support multi-level paths

[rallisf1]

Known bug: If you create multiple pages with the same url (slug) the router will always fetch the first one it gets from the db. Possible solutions:

• On page creation and renaming check if the url already exists and return an error.
• Refactor to take into consideration the full_url

Please merge AFTER the builder PR.

closes #291 ref https://github.com/primocms/builder/pull/5

[mateomorris]

@rallisf1 could you merge this into next instead? Thanks

[rallisf1]

ok