Renaming: display->view, delete_annotation! -> delete!

This is a bit scary, but I've been thinking about it for a long time and decided before JuliaCon that it was time to do this. Basically the problem is that `using ImageView` has been resulting in a conflict with the `Base.display` function. So this renames `display` to `view`. It also cleans up working with annotations: they used to be returned as a `Uint`, but this wraps them in a type so that functions like `delete!` can be used.