Do not add artificial created_at fields

Make sure not to produce/use artificial created_at fields when the
retrieved entity already includes such a field.
Description of potential issues with the data
Retrieve 5 pages of old content by default.

When doing multipage requests for large projects, several pages
are being retrieved over and over, and concequently several
queries are being performed over and over. This commit restricts
the number of pages of old content being retrieved to make
event processing more lightweight. Additional data can be
retrieved using the ght_retrieve_repo command which always
retrieves all repository data.
Include the max method in the class