Fix TypeError exception in db.py on add activities

Fix TypeError exception: tuple indices must be integers, not str.
README knits
Do not create new connection for each notification

This typo caused creation of new dbus connection every time a
notification was sent.
renamed function for storing tag autocomplete preferences
fixes #80
Merge pull request #121 from sebastian-leidig/master

corrected function name: set_tags_autocomplete -> update_autocomplete_tags
Merge pull request #119 from tbabej/Fix_typo_bug

Typo notification_conn -> _notification_conn : Do not create new connection for each notification
Merge pull request #112 from msize/patch-2

Fix TypeError exception in db.py on add activities