add owner role support (#1340)

This PR adds support to Owner roles.

The owner role has a similar access level as the admin, but it has the power to delete the account.

Besides that, the role has the following constraints:

- The role can only be transferred. So, only a user with the owner role can transfer the owner role to a new user
- It can't be assigned to users being invited
- It can't be assigned to service users

management/server/http/accounts_handler.go

@@ -40,7 +40,7 @@ func (h *AccountsHandler) GetAllAccounts(w http.ResponseWriter, r *http.Request)
 		return
 	}
 
-	if !user.IsAdmin() {
+	if !user.HasAdminPower() {
 		util.WriteError(status.Errorf(status.PermissionDenied, "the user has no permission to access account data"), w)
 		return
 	}