Fixes invisible list bullet issue by using a unicode char.
Show new items at the top
Don't display the channel, but keep it in the div for navigation
Upgrades rails to 4.2.0beta2

- Also upgrades omniauth-slack and some other gems.
Option to choose a team, if you're signed in more than one.

- Better session handling
- Checks for authorization while accessing item list
Highlight currently active hashtag or mention