Office 365 Compatibility

Adding code to skip the "Contacts/Lync Contacts" and "Contacts/GAL" folders, otherwise the script will crash when backing up from an Office365 mailbox.

Thusly

Traceback (most recent call last):
  File "C:\IMAP Backup\imapbackup.py", line 712, in <module>
    main()
  File "C:\IMAP Backup\imapbackup.py", line 618, in main
    fol_messages = scan_folder(server, foldername)
  File "C:\IMAP Backup\imapbackup.py", line 263, in scan_folder
    header = data[0][1].strip()
TypeError: 'NoneType' object is unsubscriptable