Add missing "author" field to Information Sources

[ribose-jeffreylau]

... then later on switch to Relaton proper.

from discussion with @maccraymer

[maccraymer]

There are other missing attributes for information sources (citations) in addition to the author. See the current ISOGR and data entry spreadsheet for all the attributes that are presently used. -Mike

[ronaldtse]

This is also related to #13 .

[strogonoff]

The reason author field is missing is that none of the existing item data exported from Java DB has author in information sources. This seems to be an omission with our YAML export. Filed isogr/register-system-transition#7