[REF] 8.0 mgmtsystem_action

The current module inherit `crm.claim` while the `state` attribute doesn't exist anymore. I made some changes to use the `stage_id` instead but I'm not so sure it's a good idea. I'm open to suggestions.
Beyond me, but I think there's a better way to get an url for a record.

Looking at the share module, it seems to do it this way (using `web.base.url` instead of `web.base_url`). 

Maybe there's a way to get a link from `ir.actions.actions`, I don't know.

Anyway, maybe it would be better for the url to come from `share`, maybe not.