Add date validation

I'm only concerned with validating issue dates here. In DSpace they
are generally always YYYY, YYY-MM, or YYYY-MM-DD (though in theory
they could be any valid ISO8601 format).

This also checks for cases where the date is missing and where the
metadata has specified multiple dates like "1990||1991", as this is
valid, but there is no practical value for it in our system.

csv_metadata_quality/app.py

@@ -1,6 +1,7 @@
 import csv_metadata_quality.check as check
 import csv_metadata_quality.fix as fix
 import pandas as pd
+import re
 
 def main():
     # Read all fields as strings so dates don't get converted from 1998 to 1998.0
@@ -22,5 +23,10 @@ def main():
         if column == 'dc.identifier.isbn':
             df[column] = df[column].apply(check.isbn)
 
+        # check if column is a date column like dc.date.issued
+        match = re.match(r'^.*?date.*$', column)
+        if match is not None:
+            df[column] = df[column].apply(check.date)
+
     # Write
     df.to_csv('/tmp/test.fixed.csv', index=False)