Manage persistent user data

[claustres]

For now imported user data are volatile, it would be great they can be persisted into the catalog:

• [x] add a specific feature service for user data
• [x] add a "Save to catalog" action in imported layers
• [x] add a "Remove from catalog" action in catalog layers

Consistent with https://github.com/kalisio/kMap/issues/55 & https://github.com/kalisio/kano/issues/53.

[claustres]

For now saved layers are not visible in globe.