Edges can now have a "class" attribute

[ulilicht]

With this commit, an Edge-Class can be added to an Edge.

Usage:

graph.setEdge(1, 2, {
        label: 'your label',
        class: 'great-edge special-edge',
        lineInterpolate: 'basis'
      });

Would it be possible to accept the request or is there any other possibility yet to realize classed edges?

[ulilicht]

Please don't merge the second commit, this was intended to be private.

[dey-dey]

@ulilicht create a new PR without the second commit?

[cpettitt]

Fixed in #151.