Drag-and-drop step reordering

As of trainer version 0.3.1.53, you can now reorder steps just by dragging them to a different position in your journey.

Simply choose a step in your journey, click and drag it, and drop it in the space where you want it to end up.

Trainer version 0.3.1.56 adds a bunch of nice usability touches to make it a better, smoother experience. With trainer 0.3.1.57, dropping outside of the step list will restore the step to its original position.