improve module re-ordering within pathway

[franzenr]

Currently, in order to re-order modules within a customized pathway, users have to repeatedly click an up or down arrow to move the module one slot at a time until it reaches the place they ultimately want it (unless reordering based on module dependencies, in which case there is a one-button click to fix all issues).

This isn't a huge issue when only moving a module one or two spots, but becomes tedious quickly when trying to move modules a large distance within a long pathway.

A drag and drop interface, or other solution, would be desirable here.