Set auth subject source via leader / 008

Fix for subject authority records import ("source : Property is required but was missing"). Checks for record type (bibliographic or authority) using leader position 6, and if authority uses 008 position 11 for source as per:

http://www.loc.gov/marc/authority/ad008.html

Sets source to "Source not specified" for bibliographic records without an ind2 or subfield $2 value.