moving a selection shouldn't count as a change

[mimshwright]

I don't know if it's possible to only refresh when certain changes are made, but it seems like when you move the object that you have selected, it shouldn't redraw because nothing is actually being changed. If this is too difficult to fix, it's not a big deal.

(I do kinda like the idea of a refresh button though as per #200)

repro:

1. select a big image
2. drag it around

Expected: The plugin shouldn't refresh

Actual: The plugin refreshes and (for large images) can freeze