OPENNLP-1623: Add more test cases for Coref component

[mawiesne]

Change

• adds a ton of new test classes
• adjusts TrainModel interface to return the trained model
• fixes several undetected class cast bugs due to '@SuppressWarnings("unchecked")' cover-up
• makes CorefTrainerTest (somehow) pass
• makes classes named Enum be actual enums

Code-Coverage

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[rzo1]

Overall, it looks good to me. More tests, less bugs ;-)

I have added a question regarding the source (and license?) of the huge acronym txt file.