Make p-item and skill card icons draggable again

[surisuririsu]

Previously, p-item and skill card icons were draggable because the UI involved dragging in entities from the entity bank. However, this was removed in #7 in favor of a picker modal.

This leaves it slightly inconvenient to swap the positions of p-items or skill cards in the loadout, so it would be nice to make them draggable again, just for rearranging.