Added a "close on disconnect" option 

Added a close-on-disconnect option.  This enables/facilitates automation (for example: you can invoke a connectbot shortcut from tasker and this will ensure that the screen isn't stuck on the disconnect prompt).

Close-on-disconnect will not take effect if stay-connected is checked.

![screenshot_2013-06-19-07-02-29](https://f.cloud.github.com/assets/746276/673056/3f85343a-d8a6-11e2-9a5f-70935c9f2154.png)

Slightly modified from [peffreyking's branch](https://code.google.com/r/peffreyking-connectbot/source/detail?r=6db98fe935581f27fd86a50748497a45ce53b9f3&name=quick-disconnect).