Clear images in gh-uploader when navigating between items
Clear images in gh-uploader when navigating between items

closes #6198
- clear img src in gh-uploader when navigating to item with image
- always reset uploader component when new image is not empty

TryGhost/Ghost-Admin,TryGhost/Ghost-Admin,airycanon/Ghost-Admin,JohnONolan/Ghost-Admin,acburdine/Ghost-Admin,acburdine/Ghost-Admin,JohnONolan/Ghost-Admin,airycanon/Ghost-Admin,kevinansfield/Ghost-Admin,dbalders/Ghost-Admin,dbalders/Ghost-Admin,kevinansfield/Ghost-Admin