Enable automatic close on disconnect (for automation)

Currently: When launching a shortcut connection from Tasker or other automation app, the app stays in focus on the phone screen even after disconnecting.  This pull request is to allow the app to  automatically disconnect and close when a connection has been terminated.  It respects the 'stay connected' flag.  

![image](https://f.cloud.github.com/assets/746276/2505921/4cf56c32-b39f-11e3-8a4b-11009d038a5b.png)

This pull request adds a 'Close on disconnect' option

![image](https://f.cloud.github.com/assets/746276/2505928/759fecac-b39f-11e3-8c59-dd3d620da11e.png)

This will allow the connection to disconnect without prompting, which is favorable for automation.  

*This patch was originally posted [here](https://code.google.com/r/peffreyking-connectbot/source/detail?r=6db98fe935581f27fd86a50748497a45ce53b9f3&name=quick-disconnect) and [here](https://github.com/connectbot/connectbot/pull/23)*