Refactor gfln_parse_footer_links()

 * Renames gfln_parse_footer_links() to gfnl_amend_links(). This is to make it more general, since we don't care where the links are located. The fact they are from a footer has already been decided by filtering genesis_footer_output.
 * Moves the domains grabbing code to own function.
 * Domain grabbing now includes a trim call.