add feature to display resources being edited

add a way to see on the view - which are the resources open in the editor (just a edit icon as on the screenshot below). Double-clicking in the tree on the resources already open will close them (it is too easy to open new resources now - too many tabs on the editor)

![screenshot from 2014-09-11 13 13 51](https://cloud.githubusercontent.com/assets/1168053/4233046/740a08be-39a5-11e4-92a2-06c326aca378.png)

That was really the last one for today ...
C.