Allow annotator to handle images of different resolutions in the same sequence

[mattdawkins]

[mattdawkins]

Example - https://data.kitware.com/api/v1/item/5e96774d9014a6d84e0da4c7/download

[subdavis]

I think it would be easy enough to support this provided the images in the set aren't intended to have world alignment information, i.e. if they aren't intended to be tracked.