Added mouse position plugin for mpld3 backend
Added mouse position plugin for mpld3 backend

basnijholt/holoviews,mjabri/holoviews,vascotenner/holoviews,basnijholt/holoviews,ioam/holoviews,mjabri/holoviews,vascotenner/holoviews,ioam/holoviews,vascotenner/holoviews,mjabri/holoviews,ioam/holoviews,basnijholt/holoviews