Drag and Drop, Save to a Collection

Really proud of the work @ksylvest and I did on subtlety for drag and drop in the new @pose app.

The key was tracking the user's finger to the bottom 1/3 of the thumbnail. Made a world of difference in maintaining visibility vs. our initial instinct, which was to track it to the center (or, like Apple in the Photos app, tracking to whereever the user initially touched the original item).