AD filter returns a Pandas DataFrame

[JulienPeloton]

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Linked to issue(s): Closes #144

What changes were proposed in this pull request?

The filter returns a Pandas DataFrame instead of a Spark DataFrame (more convenient for database operations later, as it avoids a toPandas to be performed).

The test suite has been extended as well.

How was this patch tested?

Manually + CI

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: +4.20 🎉

Comparison is base (d263622) 63.28% compared to head (1549a66) 67.49%.

❗ Current head 1549a66 differs from pull request most recent head 7c0c0b0. Consider uploading reports for the commit 7c0c0b0 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #145      +/-   ##
==========================================
+ Coverage   63.28%   67.49%   +4.20%     
==========================================
  Files          17       17              
  Lines         523      526       +3     
==========================================
+ Hits          331      355      +24     
+ Misses        192      171      -21     

Impacted Files	Coverage Δ
fink_filters/__init__.py	100.00% <100.00%> (ø)
fink_filters/filter_anomaly_notification/filter.py	93.54% <100.00%> (+75.69%)	⬆️

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