Account: Don't use soup_session_send_message
Use one global SoupSession
ITimeline: Add some whitspace
DefaultTimeline: Synchronize unread_count and tweets

When we set the unread count to 0, mark all the tweets as seen.
NotificationManager: Add function to withdraw notification
TweetListEntry: Add notification_id field

And withdraw the notification if the seen flag gets set to true
MentionsTimeline: Set the mention's notification_id flag
Account: Uninit properly
compose-window: Add sizegroup back

Turns out, it *is* needed.
SettingsDialog: Fix alt+num shortcuts
DMThreadEntry: Add field for notification id
DMThreadsPage: Return the id in notify_new_dm
TweetListEntry: Nullify notification_id after withdrawing
DMThreadsPage: Bundle notifications
Also withdraw notifications from within the DMPage
DMThreadsPage: Set the correct notification summary