fix the import of `xsd:date` values
fix the import of `xsd:date` values

For dates we have to use a slightly more advanced parser than the
standard `DateField` parser which does not allow some correct `xsd:date`
values with timezones, such as “2012-08-22Z” or “2012-08-22+02:00”.
MiltosD/CEFELRC,zeehio/META-SHARE,JuliBakagianni/META-SHARE,zeehio/META-SHARE,JuliBakagianni/META-SHARE,zeehio/META-SHARE,JuliBakagianni/CEF-ELRC,MiltosD/CEF-ELRC,MiltosD/CEF-ELRC,zeehio/META-SHARE,zeehio/META-SHARE,JuliBakagianni/META-SHARE,MiltosD/CEFELRC,JuliBakagianni/META-SHARE,MiltosD/CEF-ELRC,MiltosD/CEF-ELRC,JuliBakagianni/CEF-ELRC,JuliBakagianni/CEF-ELRC,MiltosD/CEF-ELRC,MiltosD/CEFELRC,JuliBakagianni/CEF-ELRC,JuliBakagianni/META-SHARE,zeehio/META-SHARE,MiltosD/CEF-ELRC,JuliBakagianni/CEF-ELRC,JuliBakagianni/META-SHARE,MiltosD/CEFELRC,JuliBakagianni/META-SHARE,MiltosD/CEFELRC,MiltosD/CEFELRC,MiltosD/CEFELRC,zeehio/META-SHARE,JuliBakagianni/CEF-ELRC,JuliBakagianni/CEF-ELRC,MiltosD/CEF-ELRC