[FEATURE] Check completeness of hierarchies during import

[srcds]

When importing generalization hierarchies for multiple attributes it can easily happen to confuse different attributes and hierarchy files.

Example:

• Start ARX and open the "example.deid" project provided as an example in the "data" folder (https://github.com/arx-deidentifier/arx/blob/master/data/example.deid)
• Click on the column “occupation” and click on “File -> Import hierarchy”
• Now we simulate a user error by selecting the hierarchy file “adult_hierarchy_workclass.csv” (https://github.com/arx-deidentifier/arx/blob/master/data/adult_hierarchy_workclass.csv) instead of the hierarchy for occupation (I think it can happen quite fast to confuse them)
• Complete the import
• When you try to anonymize the dataset the following message will appear:
  

Now the user realizes that he/she might have made a mistake during importing the hierarchy. However, now, the old hierarchy for the attribute is already overwritten and lost.
It would be nice if ARX displays a Warning when you want to import an incomplete hierarchy during the import.

E.g.:

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Attention

The hierarchy you are about to import does not cover the full range of the attribute "occupation": hierarchy does not contain a transformation rule for value "Sales"

Continue with import?

[Yes] [No]

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This request is related to #347

[prasser]

Implemented. Closing.