Add a listener for addInitial() events in the-graph-graph.js

[townxelliot]

There is a listener for removeInitial() events (line https://github.com/the-grid/the-graph/blob/master/the-graph/the-graph-graph.js#L107), but no listener for addInitial(). This makes it difficult to draw ports differently depending on whether IIPs are connected to them, as there's no port redraw when IIPs are added, only when they're removed. Adding a duplicate of line 107, replacing removeInitial with addInitial, would do the trick.