Update seaborn.categorical.py to allow adjusting the marker colors of the box plot within a violin plots

[Cortexan]

In the current version, it is not possible to manually set the marker colours for the inner box plot appearing within a violin plot via passing "markerfacecolor" or "markeredgecolor" to "inner_kws" as key-value pairs.

this is because the "dot_kws" parameters "markerfacecolor" and "markeredgecolor" are directly set to "w" when the violin plot is generated:

`

on lines 1139-1148 of categorical.py:

            dot_kws = {
                "marker": marker,
                "markersize": box_width / 1.2,
                "markeredgewidth": box_width / 5,
                "transform": trans,
                **inner_kws,
                "markeredgecolor": "w",
                "markerfacecolor": "w",
                "color": linecolor,  # simplify tests
            }

`

this is resolved by removing the explicit colour settings from dot_kws, resulting in a marker that defaults to all white if no parameters are passed, but adopts manual settings when they are:

`

replace lines 1139-1148 of categorical.py with:

            dot_kws = {
                "marker": marker,
                "markersize": box_width / 1.2,
                "markeredgewidth": box_width / 5,
                "transform": trans,
                **inner_kws,
                "color": linecolor,  # simplify tests
            }

`

to reproduce the error and more desirable functionality, pass the following inner_kws parameter to a violin plot, once before and once after the modification to categorical.py described above:

inner_kws=dict(box_width=3, whis_width=1, color=".5", marker="o", markerfacecolor="k", markeredgecolor="#ff20ff", solid_capstyle="round"))