Actions for thread entries

##### Thread action button top-right
![screen shot 2014-10-10 at 8 42 18 am](https://cloud.githubusercontent.com/assets/672074/4593177/d69e81a4-5083-11e4-9969-ac027199549b.png)

##### Drop down with extensible actions (think plugins!)
![screen shot 2014-10-10 at 8 43 48 am](https://cloud.githubusercontent.com/assets/672074/4593185/e86276e8-5083-11e4-8947-13e3247983cd.png)

##### Popup dialog with raw email headers
![screen shot 2014-10-10 at 8 43 58 am](https://cloud.githubusercontent.com/assets/672074/4593190/f3356f4e-5083-11e4-8616-70bbe9ed96df.png)


Add `$_actions` as instance var