3d removal of background

https://www.notion.so/qim-dtu/3D-remove-background-function-fac8e64da886429eacd9520bc7be0610?pvs=4

implemented into existing filters framework

qim3d/processing/filters.py

@@ -14,6 +14,7 @@ __all__ = [
     "Maximum",
     "Minimum",
     "Pipeline",
+    "Tophat",
     "gaussian",
     "median",
     "maximum",