IDEView: set active pane state [#80356544]

Set focus state of IDE when window loses and gains focus, user switches panes, tabs and apps.

[Focus is not preserved when app, pane and tab is switched](https://www.pivotaltracker.com/story/show/80356544)

https://github.com/koding/kd/blob/master/src/core/windowcontroller.coffee#L134