Improve session handling #9

Created a session-factory bound to connexion's underlying sqlalchemy engine and instanciated 2 separate sessions - each for api and sync.

Tests for setting/getting active source succeeded, so assuming that there is no need of calling commit() before the query. Since each session is created in the according context / thread, this approach should also be thread-safe but couldnt verify yet.

Need to retest, thus marking this mr to draft.

src/aura_engine_api/sync.py

@@ -132,6 +132,7 @@ class SyncJob(threading.Thread):
                     for entry in entries:
                         try:
                             session.begin_nested()
+                            entry["trackStart"] = entry["track_start"]  # TEMP FIX
                             entry = PlayLogAPI.from_dict(entry)
                             playlog = PlayLog(entry)
                             playlog.is_synced = True