Factored SideHistogramPlot out from DataHistogramPlot
Factored SideHistogramPlot out from DataHistogramPlot

Introduces the concept of SideViewPlots, which hold reference
to the main plot.

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