`Alias` and `AliasContent` objects should not have `get_absoulte_url` methods

[fsbraun]

Bug: Edit alias context menu of alias plugin

When no alias content object for the current language exists, the "Edit alias" menu entry redirects to something like admin/cms/placeholder/object/5/edit/3/None.

Code inspection shows that the context menu uses the get_absolute_url method of the Alias object.

Way forward

According to the Django docs, get_absolute_url should calculate the canonical URL of an object. I argue that aliases should not have a canonical URL, since

• they represent fragments which are not to be offered to the end user independently
• all URL returned by the current implementation refer to admin sites which - by definition - are unreachable for non-staff users.
• the "View on site" link in the admin's object tools

I propose to

• Remove the methods from both Alias and AliasContent
• Replace the "Edit alias..." plugin context menu URL (now the "canonical" URL) with a real edit URL
• Replace the admin object tools "View on site..." by "View content..."

Thanks to @vasekch for pointing this out on slack.