Util: preliminary implementation of make_tracking() method. It can't handle statuses with no ID, though.
Timeline, StatusStorage::*: API CHANGE: now contains() method must accept statuse objects with no "id" field. They must be treated as "not contained".
Previously, those ID-less statuses make contains() method croak. This behavior has been changed.
t/Util_make_tracking.t: fix test. Pass the test for make_tracking() func.