Werk #10031: Warn about editing rules which conditions are not valid anymore

When a rule is opened for editing and an the rule edit dialog detected an invalid previous value, it prints a warning message about this to the user.

The same is now done for the rule conditions. In case e.g. a rule refers to a tag group or tag that does not exist (anymore) in the current WATO configuration, the dialog shows a warning message instead of silently dropping the invalid option as it was done before.

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