Added utility to apply topological sorting to Overlay layers
Added utility to apply topological sorting to Overlay layers

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