[Bug] Colour Mapping of Base16Theme Differs from Default Theme

[kevinmatthes]

This issue is related to #79.

When working on #81, I noticed several major differences between the ways the colours are mapped in the default theme, zee-gruvbox, and how the colours of the Base16Theme-defined schemes are mapped onto the editor's components.

One example is that the highlight colour for the current line is fetched from the selection colour in zee-gruvbox, giving the status bar a colour on its own, while all other themes are defined such that the selection colour is on its own while the current line and the status bar share their background colours.

Since this procedure is not uniform I would consider this a bug.