Initial python3 changes

Mostly just updating libraries, removing string encoding/decoding,
fixing some edge cases. No new functionality was added in this
commit.

lib/apscheduler/jobstores/sqlalchemy.py

@@ -1,11 +1,11 @@
-from __future__ import absolute_import
+
 
 from apscheduler.jobstores.base import BaseJobStore, JobLookupError, ConflictingIdError
 from apscheduler.util import maybe_ref, datetime_to_utc_timestamp, utc_timestamp_to_datetime
 from apscheduler.job import Job
 
 try:
-    import cPickle as pickle
+    import pickle as pickle
 except ImportError:  # pragma: nocover
     import pickle