Fix missing proceedings from Kenya hansard

The check for new sources was only considering whether the name of the link
had been seen before, regardless of whether that name was from the senate
or national assembly list pages.  This fixes that check so that the list page is
taken into account. This change means that we find 61 missing proceedings.
Does this change need another database migration to make sure uniqueness is enforced at the database level (and remove the unique constraint on the name column)?