Fixed collab redraw error

Solves issue #63 

Needed to initialize "var draw = false;" in drawEachCollabForEvent() like we do in drawEachHandoffForEvent(). Previously it just said "var = draw;"

To test, repeat the use case cited in the issue (below) and also try some other cases of drawing collaborations and dragging events around.
Draw 3 cascading events. Draw collabs between vertically adjacent events. Drag event 1. In the bug case, both collabs would redraw on top of each other so it looked like collab 2 was missing. Should not happen anymore.