Moving labels for clearer reading.

![RabbitMQSim-labels](https://f.cloud.github.com/assets/1858212/245251/b4f73742-8a7a-11e2-81bc-b5cc26854aa2.png)

The labels for nodes, and edges were somewhat hard to read, so I moved
them to show up below the nodes in the toolbox, as well as the nodes
and edges in the drawing area.