Efficiency upgrade, critical bug fix, color options

The IB collision algorithm is now more efficient thanks to an improved search radius. This in turn exposed a critical bug where long recursive sliding could result in tunneling through mesh elements that were not originally considered at the initial point of intersection. This has now been fixed. Finally, both swarm and ibmesh colors can be specified as an attribute for plotting.

Other more minor bug fixes and improvements are included as well, including a fix for 3D plotting which was broken in some installations.