data handler FIR filter

Create a new data handler that uses FIR filters. The structure of this data handler should be as similar as possible to the kz filter data handler.

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created merge request !295 (merged) to address this issue

mentioned in merge request !295 (merged)

mentioned in commit f68ecb48

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closed with commit f68ecb48

closed with merge request !318 (merged)

mentioned in commit 1634c669