Enabled hovering over line to get probe number in plot_traj (mpld3)

Used Dan's plugin LineLabelTooltip made for mpld3 to enable this functionality in iPython notebook plots obtained with mr.plot_traj
New mpld3 syntax
Merge pull request #44 from vallard1/patch-1

Experimental Feature: Enabled hovering over line to get probe number in plot_traj (mpld3)