Added optional tableViewCanReorderRows: delegate method; renamed other delegate methods and properties

Also cleaned up code to be more idiomatic (removed non-profixed IVARs, using properties instead).
Cell dragging improvements

1) Cell dragging limits are now the actual table limits (instead of some arbitrary extra value)
2) Dragging position is calculated by offset now, so the zoom in/out animation is always consistent (and not dependent on which Y position on the cell you did the long press)