Added ElementPlot.init_glyph method to be overridden by subclasses
Added ElementPlot.init_glyph method to be overridden by subclasses

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