[Conkeror] breaking change: themes

[John J Foerch]

Hi all,

  In order to make Conkeror compatible with native toolkit theming,
Conkeror's themes have undergone a big rewrite.

 * Conkeror no longer specifies its own gui colors.

 * The blackened theme no longer exists.

 * It is no longer possible to theme scrollbars.

  From now on, the right way to change Conkeror's gui colors is to do so
at the OS level, for example, with a GTK theme.

  Sorry for any inconvenience.

-- 
John Foerch