Add function to detect repeated entities

[eriknovak]

This PR adds the detect_repeats input parameter to the extractors, which forces the extractor to go through the input text and find any missed entities. This is done in the following way:

1. Uses the extractor to identify the entities within the text based on the provided labels
2. Search for any repetition of the identified entities within the input text that were missed
3. Return all found entities

The functionality is also tested in new unit tests.