theme_void() equivalent

[Nikita-Pavlenko]

For pie charts, for example, we does not need background, axis and the other things except of chart itself.

Currently this could be done with

themeClassic() + theme(axis="blank")

but it would be great to have ggplot analog of theme_void()

[OLarionova-HORIS]

Added: #833

[alshan]

Added in 4.0.0, soon in Kotlin API.

[alshan]

In LPK 4.4.2 : https://nbviewer.org/github/JetBrains/lets-plot-kotlin/blob/master/docs/examples/jupyter-notebooks/f-4.4.2/theme_void.ipynb

Unfortunately at the moment themeVoid() is not fully compatible with "flavors": #858