Do not make object inheritance

This patch removes these lintian warnings:

Warning R0205: Class 'X' inherits from object,
can be safely removed from bases in python3 (useless-object-inheritance)

offlineimap/folder/Base.py

@@ -26,7 +26,7 @@ from offlineimap.error import OfflineImapError
 import offlineimap.accounts
 
 
-class BaseFolder(object):
+class BaseFolder():
     __hash__ = None
 
     def __init__(self, name, repository):

offlineimap/folder/LocalStatusSQLite.py

@@ -25,7 +25,7 @@ import six
 from .Base import BaseFolder
 
 
-class DatabaseFileLock(object):
+class DatabaseFileLock():
     """Lock at database file level."""
 
     def __init__(self):