This PR adds plotting classes for two Bokeh chart types, Bars, which already exist in matplotlib and box plots, which has also been added for matplotlib. Currently the Element name is BoxWhisker but I'd appreciate something better that's not BoxPlot (since that kind of breaks our naming convention). The PR is not quite ready but it already mostly works.
Here are some demos of the new supported plots: Bokeh Charts Notebook
Note: Deprecates the AdjoinPlot.subplot_size and border_size plot options
Ok, tests are passing now so I'll merge.
Edit: Having skimmed over the changes and additions, they are look ok to me. I will note that although the title of the PR is currently 'Bokeh Charts', other things are happening here (e.g adding