Copy Annotations

[matt-deboer]

This allows copying annotations from one image to another. (Implements #52)

1. Annotations from the current image can be copied to the prev or next image using the new navigation buttons in the upper right: (propagate-previous, or propagate-next)
   
2. Annotations can be copied from another image (by ID) to the current image using the "copy annotations" button on the left of the annotator view:
   

These are leveraged via a new POST /api/annotator/data/{image_id} method; this method accepts both add_annotations (array of annotations by ID to add to the image),
and add_annotations_from (array of image_ids from which to copy annotations). This may not be the best place for this, but it also seemed wrong to overload the current POST /api/annotator/data method...thoughts?

[jsbroks]

@matt-deboer I've changed quite a few things. Once again let me know if it works for your use case

[matt-deboer]

This should work fine.

It is a little tedious to click the dialog box to copy from the previous image, but I think that will go away with #57.

[azmathmoosa]

Is there no way to move an annotation after having it copied? In many cases, there are images that are the same except that the object has moved to the right. One can copy the annotation but can't move it at all. Hence this feature will be much more useful if we could do that. If I were to edit code, which file should I look to implement such a feature?