Deprecate NL SoFiNumber fields and add BSN fields.

[benkonrath]

Ref #150

[codecov-io]

Codecov Report

Merging #314 into master will decrease coverage by <.01%.
The diff coverage is 97.5%.

@@            Coverage Diff             @@
##           master     #314      +/-   ##
==========================================
- Coverage   96.28%   96.28%   -0.01%     
==========================================
  Files         156      156              
  Lines        4389     4415      +26     
  Branches      592      592              
==========================================
+ Hits         4226     4251      +25     
- Misses        102      103       +1     
  Partials       61       61

Impacted Files	Coverage Δ
localflavor/nl/forms.py	100% <100%> (ø)	⬆️
localflavor/nl/models.py	100% <100%> (ø)	⬆️
localflavor/nl/validators.py	98.63% <93.33%> (-1.37%)	⬇️

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