filters: Add Unicode normalization to CleanText
filters: Add Unicode normalization to CleanText

With a default to 'NFC'.
This is inspired by python-ftfy, which has a nice explanation of the modes:
https://github.com/LuminosoInsight/python-ftfy

I think K is too strong to be a default, however C has zero visual differences
and should be the most common way to represent Unicode characters.

frankrousseau/weboob,sputnick-dev/weboob,willprice/weboob,RouxRC/weboob,RouxRC/weboob,laurent-george/weboob,Konubinix/weboob,Konubinix/weboob,frankrousseau/weboob,nojhan/weboob-devel,frankrousseau/weboob,laurent-george/weboob,willprice/weboob,willprice/weboob,nojhan/weboob-devel,sputnick-dev/weboob,sputnick-dev/weboob,laurent-george/weboob,RouxRC/weboob,Konubinix/weboob,nojhan/weboob-devel