[Icons] Adding references to retina versions of new icons
[Icons] warning-overlay.png → invalid-reference-overlay-16.png
[Icons] folder-overlay-16.png → assembly-reference-overlay-16.png
[Icons] project-overlay-16.png → project-reference-overlay-16.png
[Icons] closed-folder-16.png → folder-closed-16.png
[Icons] open-folder-16.png → folder-open-16.png
[Icons] closed-resource-folder-16.png → resource-folder-closed-16.png
[Icons] open-resource-folder-16.png → resource-folder-open-16.png
[Icons] md-addins bump