Consider `mn` and `mfn` when parsing gender

[highsource]

In some cases the gender of the substantive is specified as mn or mfn for multiple genders.

Example for an earlier version of Tetragraph:

=== {{Wortart|Substantiv|Deutsch}}, {{mn}} ===

{{mn}} is actually not correct, as it resolves to Mongolisch. The correct version should be {{mn.}}

Example for {{mfn}} is Flipchart.

Neither mn nor mfn are currently considered by the DEPartOfSpeechHandler, in both cases this results in empty list of genders which is obiously incorrect.

I'll fix it and provide a PR.

[highsource]

Since #64 is merged, this can be closed.