open reasonable file from working set or show the no editor when an image has been deleted from the project tree.

fix 5669 [preview image] Still showing the image from prior project after opening a new project. https://github.com/adobe/brackets/issues/5669
formatting nits reported by @RaymondLim
Merge branch 'master' into couzteau/fix-5673

Conflicts:
	src/editor/EditorManager.js
EditorManager now only shows a document from the working set if we are not showing a new image already
Merge pull request #5683 from adobe/couzteau/fix-5673

fix 5673 - [preview image] After deleting an image file in side bar, selection moves to parent folder and image is still showing.