Layer improvements

[helderbetiol]

The following layer improvements are proposed:

• - For applicability with double wildcard, even if it's not the Linux pattern, apply it to the root directly above as well. Example: site/bldg/A/** should apply to everything under A but also to A.
• - Add a second parameter to the create layer command to add the filter there already.
• - Add a warning message saying the layer will no longer be visible when it has no filters.
• - Add an endpoint to the API to get the objects of a given layer.
• - Fix unable to modify slug (rename) a layer.
• - Add communication to the CLI of create/modify/delete layer.