`Color::Byte` references were before themes were introduced in the code
base. Their presence is a bug and they should all be replaced by theme
values.
Closes#124
Stop hardcoding certain component colors #124https://git.meli.delivery/meli/meli/issues/124
This adds the config option listing.sidebar_divider to set the character
used to show the divider (defaults to ' ') along with the corresponding
theme in mail.sidebar_divider which defaults to the default theme.