Adding in-between nodes should have a better UI

[clpetersonucf]

Right now, one simply hovers over the middle point of a node link to reveal the "+" button that lets you add an in-between node. However, this can often obscure other UI elements, and is generally pretty un-intuitive. A better solution may be to add a smaller, static "+" button in the middle point to make it clearer, and to improve how it behaves when adjacent/overlapping other UI elements in the creator.

[clpetersonucf]

Finally fixed in #81 💪