Set the font family in `rcParams` as default for some themes

[Gedevan-Aleksizde]

Hello, thank you for this great package!

Some themes' default font family is set as DejaVu Sans, which has large coverage for unicode -- Extended Latin, Cyrricil, Arabic, and so on. But this font doesn't cover CJK (Chinese, Japanese and Korean) fonts.
I usually set a CJK font in rcParams but these themes' default values overwrite it. I want to avoid to set the same font again. Why don't you change the default value to None

[has2k1]

In the next version of plotnine you will be able to set a default font for all your themes with

from plotnine.options import set_option
set_option('base_family',  'My Font')