remove broken plugins; add slack plugin

it comes with sane defaults -- user just needs to add room and token. user can customize pretty extensively thereafter

screenshots:
![screenshot 2014-06-12 03 11 48](https://cloud.githubusercontent.com/assets/175305/3256538/f94c4664-f219-11e3-89cc-3da3d2ca471b.png)
![screenshot 2014-06-12 03 13 04](https://cloud.githubusercontent.com/assets/175305/3256547/1ff6b376-f21a-11e3-9401-521890f97b3b.png)