added muted_alpha option for Vectfield and for Spikes (#3130)
added muted_alpha option for Vectfield and for Spikes (#3130)


ioam/holoviews,ioam/holoviews,basnijholt/holoviews,basnijholt/holoviews,ioam/holoviews,basnijholt/holoviews