'Keep selection on files' option for Stage/Unstage operations on Commit form

When user click Stage or Unstage on Commit form focus remains on the same files moved to another list.

Also there is a new page in Settings form named Behaviour
![GE-Settings](https://f.cloud.github.com/assets/1068398/236442/6eb6fc90-87eb-11e2-9710-4c0031838e38.png)