slack integration bugs

[cforster]

• the slack login shows up on the main screen incorrectly when you make a new session
• does not delete a channel when the session is deleted
• should archive once the date has passed.
• sessions could have the same name if there are two sessions on the same date, and fails if you delete and recreate. the session naming by date could also be more human readable.
• would be nice to be able to rename the slack channel after creation, if you do that now it breaks the integration.