Fire selectionChanged when working set is modified

[jasonsanjose]

Fix for #719

[redmunds]

reviewing

[redmunds]

Here's another case:

1. Open a subfolder and select one of its files.
2. Verify selection triangle is shown.
3. Close subfolder

Results: Selection triangle is continued to be displayed on the same line, so it's pointing at whatever file/folder randomly gets drawn on that line.

So, event also needs to get fired when project tree is updated.

[redmunds]

The other scenario I noticed is this:

1. Search on something using Find in Files
2. Click on a result in the list that is not in the Working Set
3. Verify file is displayed in editor

Results: The file is usually selected in the project folder, but not always. I haven't nailed down a pattern, so it seems intermittant. Also, is seems a bit slow when file is down a subfolder or 2 (which is as deep as I tested).

[jasonsanjose]

The bug about the project tree not showing find results exists in master. I'm pretty sure this doesn't have to do with the selection triangle changes.

This is intermittent based on how deep the tree is already loaded since we only load tree nodes on-demand.