Renamed fontsizes parameter to fontsize throughout
Renamed fontsizes parameter to fontsize throughout

The singular makes sense for the simple case (one common fontsize) and
makes sense when setting multiple font sizes. This change saves one
letter throughout, parses better and optimizes for the common/easy case.

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